I think one of the reasons is that ad executives will select a track that they feel 'best represents' or gels with their particuar product; then they are left with the problem of how to fit it 'neatly' into their airtime segment on television. In other words, it quite frequently happens that songs you hear on the radio, in original 'radio edit' cut form, are mutlitated and butchered down large scale for advertisements, simply for constraints of time etc.
I recently heard a Nina Simone track (a particular favourite) being spliced to high heaven for some unknown reason. The chord sequence was also totally annihilated, again for no obvious benefit.
I'm not sure if I've answered your question at all?! I would suggest that if you want the original, commercial chart released recordings of something, you should check out the song/artist either in one of their album released in a retail store, or online via a distributor such as itunes. Hopes this helped a bit.