O.K here is what I have read (and please don't ask me to show proofs of my readings! - if it makes sense, keep it, other wise throw it in the dustbin, if you like). I am no expert in the matter and I am open to educating myself in this regard. Mitochondrial DNA of many Jat tribes shows it to be common with marginalized sections of society. Mitochondrial DNA, as many of us know, is passed from the mother to the off spring. It therefore appears that the woman in Jat society came from weaker section of the society.
I have also noticed that the paternal DNA of many Indian Jats is shared by people from people living in regions outside India such as the West. This paternal DNA came to India with these travelling people and when they came to India, they took woman by force (such as what Rakesh jee is talking about).
This turned may have turned into a tradition for the purpose of marriage, where the boy and his family consider them superior to the girl's family.
Again, as I said before, please don't ask me to provide proofs - it is just a theory - which may be absolutely WRONG!