I don't think its fair to say NSMB2 is underperforming if you consider all the circumstances around its launch and the launch of NSMB for the DS. At that time there were many multimillion selling games selling at the time of NSMB's launch period, all adding to the hardware sales creating the perfect synergy to help sell the game. As big as MH3G is, its total numbers is only as much as say English Training DS at that time. Everything else for the 3DS is tiny compared to the games that was out for the DS at that time like Pokemon D/P, BA, AC, etc etc.
The game will sell better as more multimillion selling games come out for the 3DS, as big as a system seller as it is, its also heavily reliant on a big userbase to sell. Looking at the 3DS landscape in terms of software, we're really only at the beginning of big IP's being released, I have no doubt the game's sales will end at a respectable number, to judge the games total sales based on its launch period is pretty shortsighted imo.
Kobitodzukan: Kobito Kansatsu Set has shipped 100k.
Its stuff like this that makes me enjoy sales-age, you never know whats gonna surprise you.
I'm pretty sure that MHP3rdG would have sold a lot more based on the sales of 2ndG, but that is just hypothetical since 3rdG doesnt excist and never will excist. My point was not to discuss much about the game itself however, and i'm not comparing the games to eachother either, it was just to show that it is possible to focus on different things.
Electroplankton: It took quite some time for MPH3rd to reach 4.5 million copies sold, so no one expected TriG to match this at day one. The 3DS hardware have also seen a very great increase in sales since the launch of TriG. There are over 7 million 3DS systems out there now, so it should be able to support more than 1.5 million copies of TriG. Why more people buy it could be for several of reasons.
If Capcom keeps doing this, they'll never transition the MH to the next-gen, the PSP is not gonna live on forever, they're basically sacrificing the short-term gain for long term gain, which should be in any company's best interests, especially in this industry where brands can diminish quickly for whatever reason and another brand takes its spot. Expecting 4.5M for TriG, no matter the userbase is stupid, its still basically an expansion pack at the end of the day. Lets also not forget Miku underperformed according to Sega's expectations and MH3G overperformed according to Capcom's expectations.