I can sympathize with what Ian is saying in that this should have been built into the hardware right from the get go so that the add in isn't necessary, but for whatever reason it wasn't. Is this add on ideal? No, absolutely not. But there is no other way another analog slider can be added. And this isn't just a great thing for Monster Hunter. It would be great for many other games as well, such as Luigi's Mansion for example, which is the game that I am thinking provoked Nintendo into developing the addon in the first place because the original Luigi's Mansion depended on the dual analog of the GC controller so it was kinda necessary. I think when development began on that game Miyamoto and his team instantly hit that problem and that's what set the addon in motion. That's my theory anyway.
People have said FPS games were never big on handhelds, well that's probably because handhelds never had dual analog before so it wasn't really possible to do FPS correctly. The Vita is going to have dual analog, so its necessary that the 3DS does also because if it don't then VITA will hog all the FPS support.
I don't get why anyone would be shocked, though. Rumors about this have been circulating for weeks. Its not like the appearance in Famitsu came spontaneously and without warning. Where there's smoke there's usually fire so when you start seeing rumors about something there's a good chance its real. No, not every rumor ends up being true, but you shouldn't just dismiss rumors just because you don't like them.