Another way would have been to announce that they won't be giving away any hardware, that would have kept away the "it pays for it self and I get some cool goodies" crowd away so real developers could go.
The last two years, Google has said "There are no plans for giveaways." And of course, attendees actually got about $1000 worth in stuff in 2010 (Droid phone, EVO, Google TV), and $1200 worth in freebies in 2011 (Galaxy Tab 10.1, Chromebook, Verizon hotspot).
They could say there are no giveaways, but nobody's going to listen to the boy who cried wolf anymore.
They should charge the $900 and not give away any hardware without announcing whether or not they're going to. They'll be able to have $400 tickets next year without selling out as fast.