Laptops live's are generally a lot shorter, 1-2 years at the absolute max. They will never be made with all the lastest hardware that a desktop can be made with.
And I agree you got your money's worth, after all you bought a Mac. I have plenty of friends on g4 notebooks and they still work great for 80% of their daily needs.
I was perfectly happy on my almost five year old PowerBook G4 (667 MHz DVI) until about two months ago, when it developed a major fault that made it very difficult to start up. I struggled on while waiting for the new models to be announced, and my PBG4 managed to be usable (with caution and patience) until the very day I ordered my MacBook Pro.
It then decided to die for good, probably in protest at being replaced.
Eagerly awaiting the arrival of the MacBook Pro, and I'm using a borrowed iBook G4 in the meantime.
Prior to the PowerBook, I had an iBook G3, which I outgrew within a year - everything about it was too small or slow. The PowerBook was a big improvement.