There's a reason Clannad rated so high you know. people like anime that affects them emotionally. Whether it makes them happy or sad, even both. If an anime makes me cry(highly unlikely) then it's doing something right.
I don't think that just because it made you cry it deserves a 10. It has to have more than just the ''sadness'' factor in it. Unless you were expecting the anime to be that way and that the story was really good and all.
A lot of anime I have seen that I've given a 10 have made me cry...but I'd still say no. Most of those anime that I did give a 10 (if not all of them) had something more to them. Interesting characters, a compelling story, gorgeous visuals, magnificent music...if not all of these things).
For me, crying because of a series doesn't automatically make it a 10 haha. BUT, I will say that the few 10's I've seen have made me cry. I bawled with Toradora and Code Geass. Okay, not really bawled but there was some significant moistness.
Why exactly should one give an anime perfect ratings merely because it had that person in tears? "Perfection" is more than just tears, because that is rather easy to achieve (as said by early posters).