This is exactly the same as OEM computers and Windows. Microsoft have such dominance in OSes that they can't object to manufacturers making their own deals to set default search engines in browsers. It's an anti-trust issue. OEM manufacturers get paid by Google, Yahoo, etc to set the default to them.

Google can't get into the Mobile space with a platform and then expect they can enforce that their platform maintains their dominance in search. It's not competitive, and I'm sure they were expecting this to happen.

Disclaimer: I work for Y! but not in search.