Because February and April were packed with major competition in both the romance genre and just movies in general? Big idea!!!!!!
But as for your answer, in many ways, February and October have changed. February seems to be where animated movies made by smaller studios are released (Escape from Planet Earth, Lego Movie, Spongebob, Illumination's Pets project), along with romcoms and romdrams, with the occasional action movie here and there. October seems to be a lot of horror, a kids movie here and there, and plenty of adult dramas/Oscar bait. For the other months, April, and especially March, seem to be giving a bigger focus on summer blockbusters, while August could make studios put less movies in the June and July area, and January...will still be where the crap goes. With the Oscar season and limited movies rolling in nationwide, January will have the movies that the studios know are bad and won't turn a profit, but a slightly bigger push on MLK weekend. September will also be filled with movies not as bad as January, but ones that won't get a big push on the distributor's slate, with some exceptions. Now I'm fine with how the release calendar works for now, but any change is welcome!