So that's freedom no? Because it gives me the maximal capacity to choose.

To me walled garden suggests that someone else is keeping out undesirable stuff on my behalf, whether I want it or no. It's a closed platform I have to specifically subscribe to and probably pay for the privilege, that doesn't interoperate with other systems. That's how AOL worked and largely how Apple works nowadays. 

 The freedom to choose is essentially it, but, the walled garden image invokes keeping out undesirable things and being able to cultivate those that you desire in an environment of your choosing.