While I do think it can get somewhat excessive... eh. A rehash every two or three years isn't much of a stretch. Just don't buy them if you don't want them.
My main motive for getting one was to replace my run-down old Phat. It's nearly 4 years old and starting to show its age. Dead pixels all over the top screen and a rechargeable battery that lasts only around 3 hours of play time.
I started with a GBC, moved to a GBA SP, **** on the GB Micro, bought a blue DS Phat (which later **** itself), now I have a black DS Lite (and part of the hinge on it is broken).
I also never had a GB, just a pocket. Didn't really have any games worth crap for it though. Next, I mooched off people who had GBC's and later GBA's. Than moved on to GBA SP, which brought me out of the stone age. Then DS phat. And that's where I am now.
I've had my Phat for so long and it's still functional. MY cousin has just bought a Lite for a little over a year and already his L button isn't working, both hinges are loose and won't hold the screen properly.