Maybe in your universe.
Lol how are they not?
They are essentially watered down versions of Bitcoin lol with a separate block chain.
Side chains are implemented on top of bitcoin - they dont directly change the underlying protocol, only interact with it - like a wallet would.
However, some changes to core are required to support certain sidechain proposals.
Edit: Actually, when you tke into account the tokens for using sidechains ( eth, factoids, etc.) then, yeah, the lines really do begin to blur. Maybe call it alt-coin-lite?