Shouldn't void warranty
Well, under certain regulations, taking your kit apart shouldn't void the warranty in Europe at least - as long as you don't break it - but if it's a lot easier to dismantle than the PowerBook or MacBook Pro then I'd agree that it's less of an issue.
Apple in the US offers some incentives for disposing of old computers through them, doesn't it? And Europe will inevitably get around to legislation (far more civil servants can be employed that way) making computer firms responsible for the disposal of the stuff they make, as indeed car makers were supposed to be (oddly enough I've yet to see a "pop your old VW in here for recycling" box at the local dealer, but I expect it's all done with fines and charges).
Perhaps I am just cynical and see Greenpeace wanting to ride the back of publicity for an Apple product the way they did by criticising the iPhone. I didn't see any major press releases regarding the MacBook Pro 15" adoption of LED backlights from them; nor have I see a release from Greenpeace saying that the Dell XPS M2010 is an abomination of a laptop with a 150W PSU, HUGE CCFL-backlit LCD, 8.3Kg weight making it expensive to ship, etc.
My PowerBook battery was dead after 1 1/2 years; it got a lot of plugged in use which may have shortened it.