I think Android should be even "slightly" more closed. Extreme openess doesn't work for consumer products, as Linux has proven before it. I wouldn't want Android to become another Linux in the mobile world. I'm not saying Linux hasn't done wonders since it existed, but it did mostly for technology companies. It's been a failure in the consumer market, and that's because of its "too" open model. Openess is a scale, it's not an either/or thing.
There is only one other Mobile OS in the study, and that is Symbian considered before it was closed again...
Considering that there are pretty much no other open source mobile platforms, that is trivially true.