barring the time difference between the original and Pocket Game Boys, the time between releases is pretty similar:
1: Game Boy 1989 DS 2004 2: Game Boy Poc 1996 DS Lite 2006 3: Game Boy Col 1998 DSi 2008 4: Game Boy Adv 2001 3DS 2011?
If I put it like this, it's pretty obvious that there are pretty much no differences between the first two iterations of each line but cosmetic ones until the third iterations of each: the GBC and the DSi, where each line started gaining power.
Granted, the DSi has had no killer apps exclusive to it (that I've heard of), but that's more due to developers not wanting to completely abandon the rest of the userbase. And yet, you saw a lot of that during the initial years of the GBC: developers would make sure that the software that they developed would run on all available systems. Was color really THAT much better than what was in the original Game Boy? What did it really add that was so much better? The GBC eventually did start getting titles exclusive to it, and I don't know where I'm going with this so I'll stop.
But if the 3DS really is that much more powerful than the original DS, I have no difficulty imagining new software being developed for it that is actually exclusive to it, and thus completing my comparison of the [DSi to 3DS] leap to the [GBC to GBA] leap.
Obviously the comparison isn't perfect, but surely you can at least sort of see it