Ramrod, It may be true that you could alter(weaken) the extractor or in some cases just force the extractor over the cartridge case head. However that is not the way the CRF rifles are designed to work. Your sugestion could compromise the reliability and life expectancy of the extractor. In my opinion of course.
That's not Winchester's opinion. According to the Winchester manual that came with my CRF Model 70 Classic LT, the claw will slip over an already chambered round. No doubt, this is because of the relief area machined into the extractor. Removing this small amount of metal may very well have weakened it, but the steel extractor is still far stronger than any piece of brass that I'm likely to be loading into my rifle. The extractor works as advertised, and you can close it on a round without damaging anything. Ramrod is correct in saying that this can be done with the old Mausers, as well. It does not detract from the rifle, and it adds to its function.
As for Kimber Montanas, I just nearly bought one myself. If their 260 came with a faster twist, I would have. I still plan to buy one in 308, they appear to be excellent rifles. I haven't looked at the extractor on one close enough to see if it's been relieved so it can close on a chambered round, but this feature, while useful, is still not really needed.