Not really. iMessage can be used in a transparent way with non-compatible devices (it can just fallback to sms), and it merely loses its advantages. People won't care too much that it's closed, and will still use it. And it won't lock them. If their next phone isn't an iDevice, they will just go back to sms.

FaceTime doesn't fail merely because it's a closed protocol. It fails because it's a closed protocol and the application has no way to fallback to other networks in order to communicate with non-Apple people.