As for the attach rate, that's an average so 3 is extremely unlikely. I doubt many people own more than 3 games and I'm pretty sure most own less. In fact I wouldn't be surprised by an attach rate below 1. The middling quality of the 3DS games out there combined with the crazy high prices (45€ or more, I can get new Wii games for less!) won't make for a good attach rate.
When I said the attach rate for software on 3DS was about 3, I wasn't just guessing--it comes from the global 3DS numbers in Nintendo's latest round of financials that went out at the same time as the price cut announcement. The full numbers are as follows:
Total hardware sales: 4.32 million units
Total software sales to 13.96 million units
Hence the precise attach rate is 3.23 units of software sold for every 3DS unit sold. Initially this does seem quite high, but I can think of a couple of factors that help to explain it.
Firstly, the numbers are global and so incorporate Japan, which has seen better performance from the 3DS generally, but in particular has some big name titles that Western markets don't have yet, such as the latest Professor Layton game.
Secondly, the high attach rate reflects how low the hardware sales are; the 3DS user base is sufficiently small right now that it is dominated by the kind of early adopter who is willing to devote their disposable income to buying 3DS games, even if some of them (i.e. not Ocarina 3D) didn't receive extremely high review scores or come from a really big franchise. In other words, the attach rate is one figure Nintendo would probably like to see go down a bit before it goes back up, because they want to sell a lot more hardware to a much broader crowd at the new price point.