It IS the roast that is the difference. The only real difference in the beans is that some beans taste better at a higher roast than others, so they are more appropriate for espresso. Your Italian grocery coffee company may be using the espresso label for marketing purposes, but in general, espresso coffee beans can be the same beans that are used for "regular" coffee, but roasted to a French or Italian roast level, which is darker than City or Full City.
Since the advent of Starbucks, many roasts are much darker than they used to be. Dunkin' Donuts coffee, which is a Full City roast, used to be the norm, but now a French seems to be what you can buy.
I roast my own coffee and take it to just into the second crack which is, generally, a Full City roast...a point where the character of the coffee predominates rather than the flavor of the roast. There is more information about roasts at Sweet Marias where I buy my green beans, and reading through the site will give you way more of a coffee education than you probably ever wanted.
So, yes, you can use the coffee you have to make brewed coffee. It will probably be roastier than you would normally have, unless it is just a marketing ploy, in which case it will taste normal. Consider how long you have had this coffee; if it has been shelved for a while "normal" probably won't be all that great, since freshly roasted coffee is, generally, way better than old coffee. But as long as the oils aren't rancid, it is more likely just going to be bland.
I believe that the following study provides a definitive answer:
From the abstract:
High performance liquid chromatography (HPLC) was applied to the analysis of caffeine, trigonelline, nicotinic acid and sucrose in Arabica and Robusta coffee. Green and roasted coffee samples were used in this study and the degradation of sucrose and trigonelline, with the formation of nicotinic acid, was followed during roasting. Caffeine did not undergo significant degradation with only 5.4% being lost under severe roasting.
Roasting does in fact lower the caffeine content, so bolder coffees will have less caffeine if they come from the exact same bean. But even under the worst conditions, the impact of roasting is trivial compared to the impact of bean selection, brewing method, etc.
What does degrade is sucrose (sugar), which is why heavily-roasted beans tend to taste so bitter (or "bold").
Bottom line: Make your roasting decision based on flavour preference, not caffeine content. Because the effect on caffeine is so small, you really can't compare the caffeine content of light roasts vs. dark roasts categorically unless you have a controlled sample, which you don't unless you're working in a lab.
Best Answer
Actually they recently came up with a reliable test for civet coffee. Apparently a great deal of supposedly authentic stuff never actually traveled through the bowels of a cat.
According to the abstract, the levels of citric acid, malic acid, and the inositol/pyroglutamic acid are so much higher in kopi luwak that their ratios can be used to validate mixes with other beans where the proportion of kopi luwak is 50% or greater.