Keep in mind that traditionally portable consoles are kept region free as they aren't exactly confined to one location and they have no regional hardware differences such as PAL and NSTC. The first region locked portable console was the DSi which locked the DSiware games and DSi specific software. No one really gave a shit though as DS games where still region free on the DSi and no notable DSi only software was released.
It seems kind of backwards for Nintendo to region lock the 3DS considering that Sony has made all their recent consoles completely region free and Microsoft have given the publishers the choice whether to region lock their software or not.
The primary reason behind the region lock is most likely so Nintendo can ensure a "consistent" online experience by making sure users in one region don't share an online experience with users in another region. The "official" reason why Nintendo put region locks on their consoles is to reduce piracy, this is a load of bollocks though as putting a region lock on a console surely encourages homebrew/hacking.
I have since cancelled my preorder with playasia and am awaiting a hack for the 3DS so I can go back to my importing ways.