They're just trying to get sales. Dumba$$es will see the 9000, and say "oh, it's a higher number than this 8500, so it must be better." And when they check out nVidia they'll say, "hmm, what does this 'MX' mean? Oh well, its a GeForce 4, and because 4 is higher than 3, it must be better..."
There is no reason to be upset about them trying to get sales. There is nothing wrong. Sure, it may be decieving (I hate AMD's naming system that they have, but oh well, not like I can do anything about it, and it's not like it effects me at all), but most don't know which is better. As long as you know which card is better, it's not like you should care about how ATi chooses to name their products.
Everything is marketing. You can whine all you want, but you can't change it. I'm sure if you were in their shoes, you'd do the same thing. They aren't trying to impress the knowledgeable people who know the differences, they are trying to sell products.