That's true. I hadn't thought of that. They make a slight change to the thickness or add a camera, and today's idiot consumers buy it again. I confess to buying a GBA SP after getting the original GBA, but that was because I was really unhappy with how dim the original was under most real-world conditions. My original, thicker DS is fine by me for the duration. A DS without a GBA slot isn't a DS to me anyway.
Another big difference then and now is who's responsible for the console sales numbers. The NES was the mainstay of console gaming during its day. The Wii is a different animal entirely, selling so well because of its novelty value to people who never cared about consoles before. That's not to say that real gamers don't buy them, only that the numbers are way inflated by a different demographic who won't help the sales of a good, diverse Wii game library.