Because these usages of shed are assuming a few things about the objects being shed:
a. to cause (blood) to flow by cutting or wounding
b. to pour forth in drops shed tears
Both (a) and (b) require a liquid state in order to flow or drop and (c) is some form of luminance which you noted you don't actually care about. So you could say:
(a) The cyborg shed oil from its veins.
(b) The sky shed rain upon the fields.
These are non-standard in the sense that their usage is extremely uncommon but the meaning still fits.
To directly answer your question: You can shed blood, sweat and tears because they are liquids dispersed from cutting or wounding (blood) or things that pour forth in drops (sweat; tears). If anything else in the human body could do either of those things you could also shed them.
To prove the point:
A urinary tract infection has been plaguing me for days. Yesterday I shed a mere three drops.
By the way, I have no idea where you copied your definitions from but the link you gave doesn't seem to match.
(AmE, non-linguist) It's a little tricky to say would is the past form of will, as will is an auxiliary verb that doesn't conjugate normally. It does work with will as the wish meaning. Here is part of the problem, I think.
Will for the future is correct. I will go to MIT in 2 years.. If someone says I would go to MIT someday without further elaboration, I think it's not formally "correct", but just the informality of the spoken word.
The "correct" use is
*I would go to MIT if (I had the chance, the money, got in, etc.)
But I can see someone kind of saying it casually/thoughtfully
I would go to MIT. It sounds like a good thing to do.
Used to express a desire/wish, it's more in the form of
Would that I were employed and financially independent. I hate living at home still. - or I would love to live independently. (Implied: if only I could.)
Why would vs will? Will is more concrete, less conditional. I will love living on my own does not mean the same thing. It may be different for you, but in the US, will is something we ask youngsters, who have the optimism of youth:
What will you be when you grow up? Typical answer: I'm going to be a horse trainer/veterinarian/scientist/doctor/nurse/teacher/mother/father/truck driver/fire fighter/movie star, etc.
As we age, wills become woulds.
I would like to be a musician/writer/lawyer/activist/therapist, etc.
It is also seen as a less presumptuous/prideful way to express a desire. It's called a softening word.
(college student:) "I'm going to be a doctor." (Other college student:) "In your dreams! Do you know how hard it is to get into Med School?"
vs.
(college student:) "I would like to be a doctor. I hope I get in (-to Medical School.)" (Other college student:) "Yeah, so would I. That would really be great. Hey, do you want to study together?"
"This really annoys me a lot."
Yeah, I know plenty of people that let the way others speak really bother them. It drives me crazy when people say drownded or real-a-tor. Don't let on, though. It's not cool. I would (<- softening word) try to accept this as a foible of your adopted culture. Que sera and all that. Having a pre-planned reply to a particular annoyance might help. (Would you? Tell me a bit about that.)
Good luck, and welcome to EL&U. We are happy to answer questions about English.
Best Answer
Here's an Ngram chart that tracks the frequency in Google Books search results of "wrought havoc" (blue line) versus "wreaked havoc" versus "worked havoc" (green line) for the period 1800–2005:
Although "worked havoc" has, since the late 1800s, been consistently less common than "wrought havoc," both show the same hill-like trajectory, rising between 1880 and and 1920, peaking between 1920 and 1940, and declining between 1940 and 2000. This shared behavior strongly suggests that people who used "wrought havoc" understood it in the same sense that they understood "worked havoc"—as meaning "to create or produce or effect."
In contrast, the sense of wreaked in the phrase "wreaked havoc" is a rather late addition to the dictionary-approved definitions of that word. Here is the entry for wreak in Merriam-Webster's Eleventh Collegiate Dictionary (2003):
The crucial definition 3 is rather odd in that it presents wreak as an objectively neutral synonym for "bring about" or "cause" despite (1) being posed in the company of havoc in the example usage, (2) having as its only other current meanings the inflicting of vengeance or punishment and the giving of free rein to malevolent feeling, and (3) strongly suggesting to the unschooled ear a connection to the (objectively unrelated) verb wreck.
As recently as the Fourth Collegiate (1931), wreak had only one listed definition:
The Fifth Collegiate (1936) revamps its entry for wreak, producing something akin to the Eleventh Collegiate's first two non-archaic definitions, but with no hint of the crucial third definition there:
The third definition doesn't arrive until the Seventh Collegiate (1963), and it appears in a form that still suggests something dangerous about the "bringing about" that wreaking implies:
Finally, the Eighth Collegiate (1973) adopts the neutral language that all subsequent editions have retained:
As you can see in the Ngram chart, the period 1960–2000 is the period of steep growth in Google Books matches for "wreaked havoc." It appears that either Merriam-Webster recognized this trend early in its development or actively promoted it (or both).
In any case, I can't see how the skyrocketing usage of "wreaked havoc" in its sense of "caused or brought about havoc" in any way undermines prior and contemporaneous use of "wrought havoc." It also seems clear that, during the heyday of "wrought havoc" and "worked havoc," "wreaked havoc" was not widely used as an alternative to those formulations, which makes the idea that "wrought havoc" was somehow an erroneous rendering of "wreaked havoc" extremely implausible.
As a final note, I want to point out that the most widely used expression for "bring about havoc" during most of the period 1800–2005 was "played havoc" (the yellow line in this version of the Ngram chart):
The rise and fall of "played havoc" very nearly mirrors the corresponding up and down of "wrought havoc" and "worked havoc." The circumstantial evidence is thus very strong that "wreaked havoc" made its gains at the expense of the other three phrases tracked in this Ngram chart.