Since 10.4.9 + 10.4.10, my PowerBook seems to be stalling, lagging, slowing down and crashing alot more... Please, no questions about the specs of my machine, i'm more interested in seeing if there is anyone out there who believes Apple would do that?
There are still plenty of PPC machines out there, including mine which has not slowed with the current updates. It is entirely possible that advances in the OS might tax the capabilities of older machines. The sure way to find out is to revert to the last version you were happy with.
I would also check Activity Monitor to see if some program is using more CPU than it should (or if some recently added program is using it).
The short answer to your question is "No". I don't believe Apple is doing anything malicious. Their updates are processor specific and they have no reason to purposely make you unhappy. I am sure you realize that there comes a point when an old machine can no longer keep up with advances in software. I have an old G3 I still use, but I do not expect it to run 10.4.10.
Adding RAM is a relatively inexpensive way to extend the life of an old machine, but the simplest way is to just stay at the OS version where you happy. Best wishes.