Yeah, for example, Android Google devs do not take patches from other devs, and do not open Android til "its ready".
Other devs, mainly CM do not submit patches (its useless) and it takes a long time to support devices because you need a lot of proprietary code that needs to be available, or specs,that also needs to be available.
So yeah, but no, you definitely can lock stuff in with "open source", no problem with that.
No -- you can't. You can lock people out of your project, but FLOSS doesn't mean everyone gets to play inside your project.
The license guarantees anybody who doesn't like the way Google is doing things can take the code and start their own project around it. The forks may not be easy to keep in sync -- this shouldn't matter if you don't agree with the way Google is doing things because you'll probably stop using their work after you fork anyway.
What you want is to have Google's engineers run their project the way you want, which is NOT what open source is about at all.
Aside: You're wrong about proprietary code -- awesome people like jbq and folks from the AOSP have consistently worked with hardware vendors to open up their binary blobs. They are actively fighting for this, not using it to keep people locked into the official Android project.
So yeah, but no, you definitely can lock stuff in with "open source", no problem with that.