It's probably not a valid assumption to surmise that more than half of all OS X systems are having problems. The posts you see here are just from those who need assistance in some way. I suspect that many folks either work out problems (if any) on their own, or perhaps have few or no problems at all. Some also simply ignore or work around minor difficulties - not to say that your problem is minor!
Disconnect any externals (FireWire, USB) leave only mouse and keyboard attached, If sleep works OK, then an external device is causing the issue. If no go, repair permissions on your drive with Disk Utility, and restart. If still nogo, I have seen good results with downloading and installing the OS X Combo updater (there's one available for 10.2.8). This reload process is easy on your system, but has been a general fix-it since Jaguar, and certainly won't hurt. You would run permissions repair after that process, too.
Download and use one of the utilities that will run the various maintenance tasks in OS X. OnyX is pretty good, also Maintain1. Both are available through versiontracker.com
Come back if you are still needing answers.