Okay I guess I didn't state it as succinctly as Toby did...

If you skip the track before 1/4 is played, the "skipped" counter would go up.

If you listen to a song past the 3/4 mark, the "played" counter would go up.

So in your scenario, playing half the song would mean it wasn't skipped, nor was it played... Which kinda makes sense in an odd sort of way. If you only listen to half of a song, you didn't exactly listen to it, nor did you skip it... The exact percentages don't matter, the fact is that they should be based on a percentage of the song, and not a hard-coded 5 second timer.