why tip the hat?

I often come across the term 'Hat Tip' which now seems a pretty common one in the world of blogging.. and wondered why it was being used... -------- Ask Andy About Clothes writes - Hats are tipped, (or doffed) slightly lifting the hat off your forehead, when meeting a lady (remove your hat if you stop to talk), or to "say" to anyone, male or female – thank you, excuse me, hello, goodbye, you’re welcome or how do you do. Tipping of the hat is a conventional gesture of politeness. This hat tipping custom has the same origin as military saluting, which came from the raising of medieval Knights face visors to show friendliness. ------- It is nice to be polite, everyone should try to be polite (whatever); but is that what is intended by 'Hat Tip'.. From the minuscule knowledge that I have gained in the past four months, I don't think that is the purpose. Isn't it used when some part/idea is reproduced/expanded??