Why say thank you?

I was playing golf yesterday despite the soggy conditions because I have a serious addiction. The fairways and greens were pretty juicy, but I still managed to put up together the best round of my storied career--+5 with an even par front 9 (also a first). Anyways, I hit some great shots like my 5 hybrid to 2 feet on the 8th. One of the guys said, "nice shot." Now you would expect the proper response to be "thanks." But why couldn't I say "I know"? I didn't intend to hit a shitty shot to the green. I didn't give a quick nod to the gods before closing my eyes and hoping for the best. When I play I expect to hit good shots all the time. Otherwise, why the hell would I even play?! When Tiger hits a crazy 60-yard slice to the green because he has to, why can't the dude say, "I know"? Why has society told us we need to say thanks--completely inappropriate if you ask me. This is a capitalist nation, survival of the fittest, etc. Acknowledge you hit a great shot and let your playing partners know about it. Conceited? No way. Self confident? Most definitely.