I play tanks pretty frequently,
I've played at least two games where he's been a tank and I've been Zilean, and then I put bombs on his head and he goes in for the kill (Rammus Rolling and Malphite Alt).
But it makes sense for the better players to play carries. noobs like me don't get enough kills with Carries to get enough gold to get geared out enough to do enough deeps.
Tanks and support are definitely easier for the noobsauces.