It probably is, I personally think that 2008's got some good features, mental ray core, non destructive rigging, speed enhancements, bettter stability, smooth mesh preview, ncloth winds etc etc, which ive incorporated into my workflow.

End of the day i'm not going to stick up for them doing this, its pretty straight accross the board for every software, probably due to if they left a version for a while (say 2years) as they develped various bits, other softwares would have incorporated theose features, look at how fast computings moving along in the past 2 years, multi threadeding, multi core (dual, tripple (with the new AMD's) and Quad) 64 bit OS, new OS's, graphics cards etc etc.

The software has to be re written to take advantage of these facts, how p£$$£d off would you be if maya had a rubbish version of mental ray, which has loads of bugs really slow, memory hungry, just because the policy is to upgrade every 2 years, bet a lot of people would jump ship

If you dont use the features then theres no worry, dont upgrade.

If people see it as an option not a necessity, which Autodesk want them to, then its fine.