Like others on this thread, our approach has been simple. If you believe in Santa, he is real. If you do not believe, the magic of christmas no longer exists. and NO ONE wants that. I repeat, NO ONE wants the magic of Christmas to stop. My jr in college at UT still believes in the magic of Christmas and still gets excited when he hears Santa's sleigh bells ring right after I finish reading the Night Before Christmas. Santa has impeccable timing. He along with our 4 other children all run to their beds and cover up their heads and go to sleep when they hear those bells...
As for why people want their kids to be grateful to Santa instead, its not about credit or gratefulness. Its about believing in the greater good and that if you are a good person then good things will come your way. Its about encouraging believe in innocence and doing the right thing and not worrying about who gets credit for it. Trust me when Santa is putting together a basketball goal AND a trampoline on Christmas Eve and doesnt get a wink of sleep before the kids wake up, he doesnt give a damn who gets credit. He just wants to see those smiles on his kids faces.