I don't think there's any dairy in twinkies or similar packaged items -- it's whipped fat, with sugar and flavorings.
But all of the items you mention contain fat, so it's possible that it's a product of rancidity.
I don't know if it's related to the supertasters stuff that bikeboy389 mentioned, but some people experience taste differently -- I can't stand bitter flavors (about 1/2 the items on the list mentioned, especially coffee, artificial sweeteners and all hopped beers), but I love sour; much more so than most other people. People also smell differently (eg, the issue with asparagus, although that one's an issue not just with sensing it), so it's possible that you're just more sensitive to taste/smells in general, or to a specific chemical compound than others.
There's a bit of trickery going on in the comparison of vinegar (acetic acid) to spirits of salt (hydrochloric acid). Your 5% (0.83 molar) vinegar has a pH of about 2.5.
You need much less of the stronger acid, HCl, to reach that same pH (2.5); in fact only 0.003 molar, a factor of 277 less.
Since you taste the anion (acetate or chloride), not the proton (H+), it's no wonder that the vinegar is much more flavorful; there's a 277 fold difference in the concentration of the flavor agent. Pick a different acid, and you'll get a different tasting anion, and a different concentration needed to reach pH 2.5.
Response to comment on taste of anions:
Your linked Wikipedia article gives the impression that the taste reception system is fairly simple, and well understood. It is neither.
Here are a couple examples of reasonably current research on the taste of anions:
The Anion Paradox in Sodium Taste Reception
Anion size of sodium salts and simple taste reaction times.
Take a look at Wikipedia's article on taste receptors. you'll see that 'bitter' tastes are subclassified by 30 or more different receptors.
Salty taste receptors (specific anion and cation) are still are poorly characterized
Research on humans is hard, so it'll probably be decades before the mechanisms of tasting are fully sorted out. Until then, consider sources like Wikipedia expositions of the current state of knowledge, rather than the final word.
Best Answer
Concord grapes, which most grape jellies/jams/preserves in the US are made from, are derived from the (US-native) "fox grape" (Vitis labrusca) rather than (Europe-native) wine grape (Vitis vinifera). Common table grapes (the ones eaten as fresh fruit) such as Thompson seedless are also derived from Vitis vinifera wine grapes.
Fox grapes have a "foxy" taste character, which is a result of the presence of the naturally occurring compound methyl anthranilate. Methyl anthranilate is a rather simple compound, and is used in many situations as an "artificial grape flavor". In many cases "grape flavored" candies, drinks and medicines are flavored not with grape extracts, but with synthetically produced methyl anthranilate. As such, these artificially flavored foods taste like Concord grapes (fox grapes), rather than table or wine grapes.
While it would be possible to come up with "artificial wine grape" flavor, the flavor profile of wine and table grapes is not dominated by a single compound, as fox grapes are. Therefore, any such "artificial wine grape" flavor would be much more expensive than artificial Concord grape flavor (i.e. just methyl anthranilate). As such, when companies reach for "grape flavor", they tend to go for the more inexpensive Concord grape flavor.
This also adds to the persistent expectation (at least in the US) as to what "grape flavored" means. Even if you came out with a wine-grape-flavored Jolly Rancher, many in the US would think it wouldn't taste right, as they expect grape flavored things to taste like Concord grapes.