Does ECC6.0 requires XI?

Dear all,

I am facing problem to position XI in our solution plan as I was asked: Is ECC6.0 required XI?

So far as I know: mySAP2005 requires XI, ECC6.0 is on mySAP2005. Can we say if customer wants to have ECC6.0, they must use it on XI?

thanks in advance.

Jing