I agree yet disagree with Batya and ramsickle.
First, yes, what distinguishes a really intense but platonic friendship between a man and a woman (or whatever is your sexual preference is) is sex. So, I see what your point is ramsickle.
On the other side of it is that a good relationship is founded on MUCH more than sex. In fact, a relationship can thrive and blossom without sex. (I would argue, however, that sex is present in the lust and infatuation that accompanies romantic interest.) I think Batya is trying to say something like that.
I can say that, once in a relationship, sex is important. Its intimacy is beyond friendship, and if it goes missing from a relationship, you will definitely feel it and know something is missing.
Okay, I will stop... discuss!