"whats the main reason to call ubuntu and mint a user -friendly linux"
As Vincent mentions comes down to personal needs & expectations using it. Ubuntu & Mint are specifically aimed at mainstream users many coming from a Windows environment. And try to create a close as possible work out of the box experience without the need of users to get their hands dirty doing the geeky things to fix it. Up & Running and Raring to Go!
Whereas disto's based on Arch & Gentoo which the user compiles the source code locally according to their chosen configuration.
And is for the more Geeky and Technically inclined.