This is the correct answer.Back in the day there were no clearos, RBAs, RDAs, etc and you had to use a little atty that was fed via a cartridge that was located where the mouthpiece is. The cartridges held little liquid and didn't feed all that great, so people started dripping juice directly on the atty instead of feeding via the cartridge.
When dripping like this you no longer need the cartridge, and the cartridge would hinder performance anyway since it would squeeze the vapor through little passages. You still need a mouthpiece though so as to avoid sucking on a hot metal atty, so people started modifying the cartridges by drilling them out, or buying tips/mouthpieces sold/made specifically for people who were dripping, to give them a nice mouthpiece without dealing with the cartridge.
So basically it's called a drip tip, because they used to be a mouthpiece made/used specifically for people dripping on the disposable attys. Over time the 510 drip tip became somewhat of a standard for mouthpieces in all vaping gear, it's purpose now disconnected from the name, but the name remains anyway.
And here is something to read if you want to have a little fun...
http://www.e-cigarette-forum.com/fo...58-i-cant-stand-drip-tips-2.html#post11381274