I have actually never seen this before. Other comments are saying its because you dont salt your water and i do so probably thats why. It also makes the taste better so overall recommended.
You can add some oil so pasta won't also stick when you have cold leftovers. I add both oil and salt in the very beginning, because there's no reason to not do that, and I have a feeling of the right amount compared to the amount of water.
And I stir once, about a minute after putting the pasta in, because something tends to stick to the bottom in the very beginning. Afterwards, it's just not necessary.
Oh, thank you for providing me with this rare knowledge. But what happens while you boil pasta, is pasta turning around and soaking the oil in. I wouldn't be doing that if it wouldn't help with pasta stickiness.
And as other people comment here, oil gets into pasta so you can have a problem with sauce not soaking in, but when I'm making something like bolognese, I sometimes pour pasta into the frying pan with the sauce, so it's getting there for sure.
I add both oil and salt in the very beginning, because there's no reason to not do that.
If you really like to impregnate your pasta, so that it won't absorb your sauce (or less well), then you are right about the there-is-no-reason-part in your answer.