the map is stored as a list in a text file (.osu). it would be hard to get over the filesize limit with objects alone since text files dont take up very much space (The Unforgiving marathon diff, a nearly hour long map, has a .osu file that's only 237kb). usually it only really matters if you are doing custom hitsounds/keysounding or storyboarding.
also, this is the actual file size limit: