We are focusing primarily (though not exclusively) on iPhone OS this year. Maybe next year we will focus primarily on the Mac. Just the normal cycle of things. No hidden meaning here.
At least this is what Mac developers option for the design award must be thinking. Is Mac OS development dying? In an answer via email, Jobs acts as customer service man saying that this time the priority is iPhone development. It's in line with John Casanta's thoughts on the Mac and iPhone OS in his blog post "iPhone software sustainability and the death of Mac software".
The Apple Design Awards (ASAS) have recognised since 1998 the success from the community to create above the average apps. Believe it or not, the first edition awarded Flash (then owned by Macromedia) most innovative app.
I think that iPhone apps deserved some extra space in the awards, perhaps best user experience, newcomer, best open source, technology adoption, game, student product,… I really hope they are reconsidered for future ceremonies.