Here is why no one wants to buy a DSi:

• "Nintendo didn't do it right the first time"
• "There's no GBA slot/It's not backwards compatible"
• "It has two cameras"
• "It costs more"

And then I'm sure there's a thousand other things some idiots can come up with. But here's why those who say the above are just conforming faggots.

It costs more

Yeah, no shit. It has two cameras (one with higher quality than the other from my understanding), more RAM, and a new SD slot installed. Shit costs money. How can you expect it to cost the same if it's adding really expensive new features? And considering the features, I think it's a fucking cheap price raise. The DSlite at launch was $130 (US) and the DSi is $170. That's only $40 for two cameras and more ram. And who can say it would have been 10 or 15 dollars cheaper if it wasn't for the dollar weakening?
The real point here is kids who grew up with the Gameboy and GBA are now adults. They don't have their mommies and daddies to give them whatever they want and they understand that shit costs money. It's because of this lousy economy and not being able to save their cash that's really making them notice the price, so they shouldn't blame Nintendo especially when they're making it cheaper than it should be.

It has two cameras

Oh god, not innovation, I beg you. "Who need two cameras?" Ok, good point, I guess. But who even needs a DS in the first place? No one. To be honest, I'd be more pissed if they only made one camera on the inside. You'd have no way of seeing how your picture turns out if you're not taking a photo of yourself.  But don't get me wrong, I don't totally support all the photoediting software and tricks, though I do think it's neat. However, I am supportive of new gameplay and all the fun things you can do in games nowadays via a camera.  Think of it, it's Eye-toy meets Gameboy camera. How can you honestly say you -hate- that?

There's no GBA slot/It's not backwards compatible

No fucking shit. How can you expect them to cram a bunch of extra components into the system AND make it smaller without taking out the giant useless gap at the bottom? Systems loose backwards compatibility kids. You can't be backwards compatible with two generations, I'm sorry. The DS lost compatibility with the GB, and no one cried then, did they?  And even if they did, I'm sure kids will get over their GBA games as fast as GB fans did, especially now that I just reminded them about it. Besides, if you want to be technical, it's backwards compatible for DS games.

Oh, and "but what about my guitar hero!"
I'm surprised you haven't thrown it out yet.

Nintendo didn't do it right the first time

Ok, you're right. Nintendo didn't make the DS perfect the first time. That's why the DSlite came out. Do you honestly think this is the first time a system has been improved upon and resold? Here's a history lesson:

The original GB comes out. It's a fat brick that everyone loves to play, but it's a bit chunky. The Gameboy Pocket is born.
(Just for kicks, I won't even say that the Gameboy Pocket's lack of color made the GBC born, but you know it did.)
So then the GBA comes out. It's a sleek new system with better graphics and, gasp, shoulder buttons! Everyone loves it, but then they realize it's a bitch to play in the dark. The GBA SP comes out. But oh wait, the GBA SP is still kinda big. The GBA Micro is born.

tl;dr GB -> GBP ~ GBA -> GBA SP -> GBA Micro ~ DS -> DSlite

But notice I'm not including the DSi in any of this. Why?
The fact of the matter is, the DSi isn't really another DS, it's a new system cashing in on the good DS name. It would be like calling a GBA the same thing as a GBC. You know that they aren't really the same system, just the same name.

Conclusion

None of these are good reasons for not wanting to get a DS. The only way I could understand people making up these excuses is that they can't afford one right now, and guess what, that's ok. Everyone understands that right now is a time of budgets and strict spending, so don't worry about not being able to afford it/getting your mom to buy it for you. But do us all a favor and stop blaming nintendo. Even though they are indeed pretty stupid with their systems and software sometimes, this is actually NOT a mistake.