I don't really understand the question. it's like asking a vegan if they would really give up eating a good steak. I mean, a good steak tastes way better than any TVP fake meat...
I'm vegan. that means I don't buy leather...period. Just because leather saddles and shoes are more practical or lasts longer than synthetic, thats not a reason to kill something for them. (and I think we've already gone into how the leather tanning process prevents the natural breakdown of leather and uses many extremely toxic chemicals)
To all the meat-eaters: would you buy a saddle made of human skin if it was found to be more comfortable and last longer than a brooks?
I know some will think that that is a false analogy, but I look at killing another animal the same way I look at killing humans. It is just wrong. especially for something as stupid as a comfortable saddle on your bike.
so for all you brooks fans, why not go out a buy a fur lined cycling jacket for the winter? fur insulates way better and lasts longer than all that synthetic polyfill crap and is way more comfortable than wool.
(in case you're going to call me on it, I don't buy wool either)

tim