As long as it's not the only way to get software on your Mac -- and I don't really see Apple doing that with their "truck" line of devices since there's probably always going to be obscure stuff that the publishers aren't going to want in the app store.

For that matter, I can't really see Adobe (for example) wanting to give 30% of the cost of Photoshop to Apple.

On the other hand, I think this is potentially fantastic for smaller developers -- it will make it easier for people to find their apps, and as with the iPad/iPhone, that 30% cut to let Apple manage all the billing issues for you might be well worth it.