I would say Ron will fall for Hermione as soon as he will have grown up a bit on the matter. I mean, he is a bit childish regarding girls at the moment, for a 15 years old ...
Well, truly, Harry does seem a bit too childish too, but since the spotlights are mainly on him at the moment, girls do come into his way (Parvati, Cho, other to come ?).
I guess it only reflects the fact that boys are usually pretty slow on the uptake when it comes to romance. Silly age, they call it