Hi. Not quite correct.
Shortly, CS's intension was originally to bring WinXP/98's menu to W7/Vista. Then skins appeared - and now it is complete alternative to a Windows Start menu itself.
Power8 is designed to work in environment where no Start Menu exists at all.
So, we're different in the core.
- they're faster (should be at least at startup) as CS is written in C++, and we write P8 in C#;
- thay have configurable themes and we don't;
- we provide access to Windows Search results and they don't (at the moment);
- we have our own implementation of JumpLists that works on WXP and they don't;
...and so on. There are pluses and minuses all over the applications. If you would like me or anyone else can provide later a comparison table on P8 and CS from user's perspective.