No, it's not surprising at all. In fact, the only thing that I'm surprised at is that it took this long for it to start to outsell everything. The 3DS is an amazing system, that is on fire, and only getting more and more popular. The DS was widely popular, with tons of great games. So when the 3DS came out, I knew it would be even better. Of course, it had a very slow start, however, I wasn't worried about it in the least, because I knew that once the DS developers migrated to the 3DS, it would not only be as popular, but could be potentially more popular.
Also, when it comes to the consoles, their generation is ending, and the new generation is beginning. So, to see those numbers get lower, and the 3DS's popular numbers get higher, to the point where the 3DS is now outselling the ending of a console generation, it's no surprise at all. In fact, it was too be expected, to be honest. So I am not surprised in the least. Especially with how much I love the 3DS, and how much I've migrated away from the 360 and PS3. They've had some good games, here and there, recently. But overall, they were growing boring and stale, as they were getting a lot of the same games, over and over again. Sure, some new, and fun games, here and there too. But, overall, I was getting bored with them, yet, for the 3DS, the hits just kept on coming, and more and more games that I wanted were coming out for it. Now, the same thing is happening with the Wii U. More and more games that I want and that interest me, are starting to coming out more and more.
However, now that the new generation is basically here. With the Wii U and PS4 out, and the Xbox One coming out in a few a days, those systems will all start to see rises in their sales, while the red hot 3DS will start to level off soon. Not immediately. Especially with this new Zelda game and bundle coming out, as well as some other games. If they can keep the flow of good games coming, it should be fine. But if the games start to slow down, then yeah, by next year, the numbers should level out. But in the short term, it's still on fire, and Zelda will be a huge seller as well. So no, again, I'm not surprised at the 3DS's success, and success over the end of a generation of consoles.