The biggest difference is between "I am a Rock" and "You'll Never Walk Alone".
"I am a Rock" is like the opposite of "You'll Never Walk Alone" where friendship and the thought of always having someone helping you and supporting you is important. In the text "I am a Rock" the attention is directed to don't get friends because you can get hurt.
"No Man is an Island" is more like "You'll Never Walk Alone".
http://favim.com/image/350224/
:)
