If the songs you're talking about are from Ayu-mi-x Non stop megamix version, yep, they finish abruptly because they have to be played in a sequel. I'm not sure if you're talking about the new RMX works that were released recently (I don't have the lengths for it) but if you're talking about older stuff check this site:
http://www.hamasaki-republic.org/dis...y_albums.shtml