I have seen the same on various models released after the 8100. I have a Cingular branded (now AT&T) 8100 and I have tested several models since getting mine as we look at accepting them into the company standards. Practically none of the devices feel like my Cingular pearl. They are not as smooth, they feel loose in the feral/socket and make more noise when used. Not certain if the earlier devices were made by a different vendor or what but I can see a dramatic difference.
Just another reason to love my pearl!