Also, yeah. The fat makes stuff tasty. Just like salt. [Which reminds me, remember when salt was evil?] I don't like [for example] the 90% ground beef -- it doesn't taste right at all without that fat.

On the subject of substituting one fat for another, it wouldn't help the flavour much. Replacing it with olive oil [just to go with your example] probably wouldn't taste as good, because it does alter the flavour. A lot.

At least, to me it does. I notice when Gremlin uses olive oil to make things instead of the not-quite-butter.

Here's the thing about fats. Fats make food taste good. It absorbs the flavors that might otherwise be water soluble and spreads them around within the food, and since it's an oil it sticks to your tongue more and hence it tastes better because you taste it more. No oil = that lovely cardboard flavor. Ever watch a cooking show where they talk about picking out a good roast or steak? They use this term, a nice marble. Which means an ideal amount of fat in the cut of meat. Enough to help the flavors come across properly. Works for lots of things. Mashed potatoes, for example. Potato in and of itself tastes like nothing. It's only when you add some fat and some salt that it starts tasting like, well, potatoes. It enhances the natural flavor. So it's not necessarily that trans fats taste good, go take a swig of whatever oil you got in the house and you'll find out what oils taste like.

I'm betting that these companies are just not replacing the trans fats with as much of some other fat - at least in flavor enhancing terms. Though I can well imagine it's likely some companies are afraid to add something else instead, because in a few years they'll probably find out that olive oil or whatever is even worse than the trans fats were.