Storm was always my least favorite X-Men character, they're about to get into the Phoenix (jean gray) story line anyway, so they could easily spend 2 movies on that and noone who didnt read the comic would have any idea what was going on. So the omission of Storm isnt that big of a deal, i'd rather see more of the cooler X-Men such as:
Archangel
Havok
Colossus
Gambit
my
though.
BMF