It's almost always nothing more than an ineffectual attempt to delay the inevitable. Eventually the change takes its course and becomes the new status quo. I have seen this process on several occasions and I frankly think it's pathetic. This is where Apple's brilliance comes in. The above process takes time.
People simply have to get used to whatever new ideas are being brought in.
By showing us what Aqua looks like some 6-9 months before Mac OS X will ship, Apple is giving the hard core user base the time it needs to cope with the big change. It's going to take X amount of time for Mac users to embrace Aqua, no matter when it happens. Had Apple waited until the release to unveil the new look, all the bitching we see now would have been taking place as the product was first being shipped. This way Apple should have the troops in line by the time it comes to hitting the streets. In the meanwhile, most of the noise being made in the Mac community is not being noticed by the mainstream press.