When you build a platform you invite innovation. 

When you provide a solution you support the product itself.

Consider: The one glaring hole in iPhone functionality life is turn-by-turn directions.  There is not (to date) any consensus as to why turn by turn directions have yet been offered, but one would assume that a third party developer would have built this solution for the iPhone platform had this been possible.

(Product) - (Capability) + (SDK) ≠ Solution

Yesterday we saw the buzz around the G1, the world's first Android powered phone.  While the phone is not as sleek or sexy as the iPhone, the functionality looks fantastic.  However, this phone has a glaring hole in it's offering - the lack of a digital media centrality.  This device has no preloaded video player.  Nearly every mid-to-high-end device with a large screen plays video. This is par for the course.  I expect my portable device to have video playback. 

As a direct result: the G1 is not the phone that has it all.  It's the phone that can have it all.

Key Takeaway

You can't outsource your core market offering to an open development platform.  I don't buy a car so that I will have something on which to place bumper stickers.  SDKs and open platforms open up opportunities for add-ons, but it is the core offering that will define the marketability of a product.