Want to actually call it an 'Android' device and/or avoid an ugly warning message to your users? [0] Gotta agree to a bunch of Google's terms including preference for their mobile app suite over others. But hey if you want some extra revenue from search you can just agree to not offer a 3rd party app store [1]. Oh also anyone in OHA (most major phone OEMs) can't make a product with a fork without getting into hot water...
To be clear I hate them both and miss the future that could have been with Maemo. As it stands however Apple is just being consistent and having full ownership, whereas Google is arguably strong-arming other manufacturers in a way that limits consumer choice, even if it is a bit more open.
[0] - AARD Code, anyone?
[1] - Smells of MSFT/Intel Bundling/exclusivity Rebates that resulted in various levels of antitrust action/settlements