Get the party started
"And with so many platforms already fighting for market share, you have to wonder if Google is much too late to the party"
I see the party not yet even started. I'm not a developer but working closely with this bunch of freaks and for years I've followed how it has given a lot of headache for developers in mobile space to produce applications on various platforms with aim to provide same user experience on different handsets.
Making the alreay messy situation messier by introducing another mobile platform is not too late at all.
In 10 years time, when we (hopefully) have less platform-specific applications and more cross-platform compatible web services (like pointed out by Charlie Clark in earlier comments) the importance of the platform is getting less.
Smaller players will die, merge or be eaten by the bigger players, leaving the strongest survivors on the market to continue the endless power-struggle.
Join the party now when mobile market is getting mature and play your cards right and in 10 years time you may well be one of the survivors.