Why are fermented dairy products pasteurised

In regard to the issues you've had with the Toffutti Sour Supreme...wait until you take it off the heat and stir it in right before serving.

If it still breaks, then try stirring arrowroot powder, tapioca starch (avail. in Asian markets), or potato starch (about a tablespoon per cup of sour supreme) into it before adding to the stroganoff. These starches (amylopectin) have a lower gellation point than grain-based starches (flour, corn, rice) which are higher in amylose and require heating to a higher temperature for the starch granules to swell and pop, releasing their starch.

OR

Try this recipe for kosher beef stroganoff where they're using coconut milk for the kosher cream sauce and say that the coconut flavor doesn't come through in the finished dish.

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.