Whilst it sounds like a valid argument to state it's all linked to study; there are some discrepancies that just don't add up.
Weekend and study implies that student's only work on weekends, even for distance lesrning that is doubtful, secondly the above chart shows some discrepancies that just don't tie up with the study hypothesis. E.g. java is just ever so slightly up from the centre point, meaning it's used almost the same amount during the week as it is used on weekend.
Considering Java's popularity with many undergraduate studies; we should have expected to see far greater use over the weekend, but that's not the case. The below the line stuff is btw considerably more popular during the week. E.g. C#, asp.net.
As for significantly above the line stuff like Haskell, Assembly, ... -- don't know about you, but I certainly haven't seen many undergraduate programmes that cover these in any significant detail; certainly not as assignments.