Porting can in fact take quite a bit to do, depending on how things are designed. If they designed their engine specifically to make the packs device independent, then yes, porting is "just" porting the engine. That said, engine porting isn't all cake and ice-cream. And since they're giving that port away to drum up sales, they have to recover that elsewhere.

I'm sure if you multiply the number of iPhone users they estimate will buy packs times the cost, the margin after covering development is much higher, even at the lower cost. The margin for the N900 is probably lower, even with the higher price per pack and lower porting costs, simply because the user base is so much smaller (and fewer are likely to spend money via the OVI store).

I'm grabbing the new packs now, and wish them well! I fully expect most things to cost a little more for us vs the iPhone. The user base is smaller by many factors, so to make up for that, costs per unit will be higher.