Its been beaten to death, but the addon is only $10 and it will likely come bundled for free with many of the games which would use it. It isn't going to be a major obstacle for 3DS owners to get ahold of one. If you have the money to purchase a 3DS game then you can just get it then, and if you don't have the money to buy a $39.99 3DS game which would bundle it then what would the point be in catering to you anyway?
No one said it would be an obstacle to get one so hop off of that horse. It's not an obstacle to buy a lot of things these days. Rather, the question is whether people
WANT to get one. There are a number of people on these very boards who don't, even for $10, myself included. I'm okay with the attachment existing. Playstation Move exists, but I'm not going to buy that either. I don't currently want the slide pad add-on, the only game it's announced for doesn't interest me (I already owned and traded it on the Wii), and I don't care that it's $10. I don't buy things just because I can. I have to
WANT it. Unless the attachment happens to come with a game I really want, I'm got going to have it. That same $10 can go towards something I actual do want like cupcakes or ice cream. Chances are the only way I'm getting a second slide pad on a 3DS is if it's included in a revision because I can't imagine there being a game on 3DS I'm dying to play that absolutely, positively requires it.
The bundling peripherals thing turned out to be an extremely successful business strategy for Nintendo during the Wii generation and it is why an unremarkable game like Wii Play somehow has managed to become one of if not the best selling video games of all time. So why wouldn't Nintendo want to replicated this peripheral bundling strategy on the 3DS or Wii U? It works and it prints money so they probably set this up deliberately.
Are you really trying to compare the Wii to the 3DS? Wii started a craze, 3DS did not. The Wii was consistently sold out everywhere for like 1.5-2 years. Nintendo had to drop the price $80 after 5 months to get people to buy a 3DS and even then, only the promise of also getting 20 free games pushed some people. Wii Play sold because it was new and casual gamers were willing literally eat **** if the word "Wii" was attached to it. It also didn't hurt that when Wii Play launched, getting extra controllers wasn't terribly easy. That's why I bought Wii Play and I only ended up liking one of those games (Tanks for the motherfucking win). I'm sure Nintendo
WANTS to replicate the success of bundling. That doesn't mean it's always going to work.