It's not the length of the song, it's the number of tracks on the album (usually). Most jazz albums seem to fall into the 5 track range, they can't sell them as .99 cent tracks because then you could get the whole album for under $5. So they randomly pick tracks (usually the long ones) so that you'll have to pay the full album price if you want it.
Albums like Karma & Black Unity fall into this as well, 1 or 2 tracks only on the album, no way they'll sell the songs to you for .99 cents.