Android IS open source. That's really not the issue people who complain about it not truly being open though.
Android DOES allow carrier locking, as well as filling up the phone with utterly stupid carrier based bullcrap. The use of the OS by the carriers to shove stupid carrier specific stuff down our throats is what is annoying to most everyone. Occasionally, those UIs are a bit better, usually no.
I personally don't think the people complaining about Android being open have merit, just as I don't think the people saying "Android is soo open" have merit either.
It's a carrier controlled OS which just has fewer regulations on it's appstore, however doesn't do centralized OS updates making development more expensive. I view it as a much more mixed bag than either "side" puts it.
On the true openness spectrum I rate it:
WinMo6/Android/WinMo7/Apple/BREW (Can't speak to Blackberry, haven't touched it).
That is true. But saying that Android is closed in an absolute manner is incorrect, and also many people raise some points that are in fact arising because Android is open (e.g. carrier locking) which need explanation.
Android DOES allow carrier locking, as well as filling up the phone with utterly stupid carrier based bullcrap. The use of the OS by the carriers to shove stupid carrier specific stuff down our throats is what is annoying to most everyone. Occasionally, those UIs are a bit better, usually no.