My wife and I have killed pronghorn in Montana (where we live and primarily hunt), along with plenty in Wyoming, and a few in Colorado and New Mexico, from late August in New Mexico to early November in Montana. Have never been able to tell any difference in flavor between antelope taken in sagebrush and "other" country, however you want to define it.
The big difference is, as many people have stated, cooling the meat down after the shot. But we have found skinning immediately isn't necessary if the weather is cool enough, say less than 50 degrees. We have killed quite a few in Montana on sub-freezing days, and left the hides on until we butchered them 2-3 days later.
One thing I learned during considerable research on big game meat is that antelope--even the older bucks--don't have nearly as much connective collagen in their muscles as many other animals--and collagen is what primarily breaks down during the aging process. (If you really want to find out a lot of details of game meat care, the University of Wyoming's meat-research department has plenty--which is where I found out about the collagen, years before websites existed. The latest info is far more easily available today.)
All that said, I also suspect there's something in pronghorn meat that makes the taste buds of a few people hate it--much like cilantro tastes like soap to some folks. Came to this conclusion after more than one occasion when several people ate the same antelope steaks, and all but one thought it was great. One of those who didn't said it tasted like "dog food," though I don't know how he knew dog food tasted.
On the other hands, have served pronghorn to a number of non-hunters who raved about how great it was.
