With the RT, yes it was indeed locked as the market pattern and target at the time (with iPad and Android tablets) have been to lock the system at the benefit of better curation and more integrated experience (well some will point out and argue that this was more of a lock-in, but obviously a Windows without malware was a goal also). The newer ARM attempt however were a complete reversal: Microsoft had dropped the focus on phone and (to an extent) tablet markets and even recent first-party Surface have unlockable boot systems, something that was impossible with Surface RT devices.