I think the only reason for that was because it was comparing numbers.
Ubuntu has been number one on distro watch for who knows how long, and now mint has beaten and surpassed the number one spot ubuntu held, I don't think it was for any other reason then this.
As far as comparing it to ubuntu goes, the main one is based on ubuntu but with changes, unless Clem wiped it out entirely in mint 12 and went for gnome 3 or MATE only with absolutely no unity and based strictly on debian with minimum parts from ubuntu which too are probably changed, how much is actually taken from ubuntu now, I don't really know anymore, I know it was based on it at one time, either way Clem has made so many changes he made it his own anyhow.
But yes comparing it to ubuntu all the time as far as another take off of it is pretty much done I think, the changes made are so different now theres not much of a comparison anymore from what I can see unless I'm wrong of course.
Gnome 3 isn't unity at all (looks a bit similar) but two different things, as is MATE from both of them.
I'm still waiting to see what happens with MATE when it matures and gets compatible totally, I'll probably switch back over to it (gnome 2 fork) instead of gnome 3, although gnome 3 was fun to play with and theme for I still prefer the old way for a working system to do all my work on, as does most folks I take it from what I read, but gnome 3 is good for plain internet use, I know I can get rotten tomatoes tossed my way for this but that's just a personal preference, I tried to use it as a working system to do my work on, but it was not as good as the old way for me, some others will disagree and the cool, it was just my preference.
I have two people using gnome 3 right now and love it more then gnome 2, I have my elderly mother using xfce and loves it the best, I switched over to xfce until MATE gets mature for my workstation now as it makes more sense for me to do so, one thing I like is the loading time, it takes seconds to load whereas gnome 3 I had to wait for the shell to load.
I do enjoy the speed