Do record releases work like movie releases? I thought that albums were kind of immune to the seasons.The new Local Natives is a fairly big record and that dropped in the dead of winter. Also, if anything, April seems to be a prestige month. In the past few years Circa Survive, Deftones, Coheed, and Explosions in the Sky have all released albums in April.
The other person that answered your question is partially right in that the albums you're citing did "ok." The rest was inaccurate. 21 came out in the US in February and is considered a sleeper hit as it substantially outdid the commercial success that was expected. Fun's "some nights" was one of the bigger albums of last year and also came out in february and nobody knew or expected it to become as huge as it was.
Yes, music does follow a "calendar" similar to movies, however, it isn't the "big budget movies may-july/ potential sleeper hits in august/horror september-october/oscar contenders no-dec" system. The music system is a slow and progressively larger build until a Super Tuesday (or several) where many high profile artists release on the same day. Once those have ceased, the following weeks are littered with smaller releases that have potential that the record companies don't want to have to compete against something that will definitely sell. Yes, you will always have a couple of big artists each month, but basically it runs a schedule. January is light on releases as it's the close of the fiscal year, so there's more interest in prepping the next year. February is a build until March, which is typically a huge monh. April is typically a slow build into may, which builds to june where there will be a huge set of releases. July is basically nothing and nearly as scant as january as it's mid fiscal year. August builds into it's final week, which is typically big as its the cutoff for grammy nominations, and continues to be high profile through september. October is bigger releases building into november, which, with june, houses the biggest releases of the year. December is basically catalogue reissues. There will be a release or two of note, but basically at that point, it's riding out thw life of the product that's already out there.