second analog stick (which hasn't been used by most games and the ones that use it, can do without it)
This is honestly a really poor argument. That's like saying the Wii doesn't need HD because none of the games are HD capable. Well duh, of COURSE none of the games are HD capable, because the system they're DESIGNED for has no HD. It's the same with the 3DS. Of course most games aren't going to rely on dual analogs when the only way to utilize such is through an unwieldy add-on that's rather impractical. If the 3DS had dual analogs built in, tons of games would use it, I guarantee you. And who knows how many developers want to make a particular game for the 3DS, only to turn around and say "eh, it doesn't have dual analogs, let's make it for Vita instead".
Hum... Not to be out of topic, but seriously, the "Let's make it for the Vita instead" line isn't going that well so far. xP
The 3DS came out with one circle pad, first buyers like me, paid 250€ for the console but the sales weren't doing so well, so Nintendo lowered the price to 150€, now, if Nintendo released a revision with a second circle pad so soon, you think most people would just be ok with that? Maybe for those that still haven't purchased one in the hopes of it getting revised it would be good, but most of the people that already have the system would complain about it.
DS Lite added more lighting settings and a sleeker look, DSi added an online interface and cameras, the DSi XL just added size.
The genre that I play the most is RPG's, and I don't really need a second analog stick for those, my favourite games are all on the Snes and PSX and they didn't use analogs, you don't need them to make good games, it might be useful in some games, but not really a necessity.
I'm pretty sure Nintendo checked all the details and people's thoughts on the console, if they didn't add one then it was most likely because they deemed it unnecessary.