I agree; also, is it canon that a brother has to be chaste? Obviously, Leliana was not.
I think Leliana was a lay sister, she hadn't taken any vows. Sebastian was a full brother, he *had* taken vows.
I don't know what canon is, but Seb *had* taken a vow of chastity.
Anders is what brought me to the BSN in the very first place, because after my first play through of DA2, I was kind of obsessed (*grin* Shocking, right?), and as I let Hawke run off with him, I was fascinated by, well, all sorts of things, and I could write a 1000 words about it, but I won't here. 
Sebastian, though-I take him with, pretty much strictly because of Alec Newman. I love that man's voice. Love.