I am surprised that having raised the question, Rebecca didn't throw out her own guess at a possible answer for either Lin's or Tebow's notoriety.
Lin is part of an under-represented group, number one, so if he has success he will automatically get a lot of attention, similar to what Yao got, and number two, he has a great 'story': Harvard kid, cut from different teams, signed for league minimum, completely out of nowhere, etc. And remember, this guy is putting up *stellar* numbers, not just really good numbers, not to mention helping the Knicks put a lot of W's on the board. You put these together and you have a powerful narrative that people can glom on to. People like excitement; excitement comes from some element of drama; drama is built around character and narrative/story line. The underdog element, always attractive, is woven throughout.
If Lin were black, I think there would still be plenty of buzz, because it's happening for the Knicks (they're starved for a great narrative having to do with their team) and he's from Harvard, came out of nowhere, etc., and his performance has been amazing. But as blacks are not under-represented in the NBA, there wouldn't be the kind of heightened focus that Lin's getting.
With Tebow, I think it's several things: 1) the fact that he really wears his faith on his sleeve, which is a big plus for many folks, especially in the South (SEC country) where he played college ball 2) the underdog element again (with so many experts saying he "can't succeed" etc.; and 3) the fact that he's a starting QB. If he were a linebacker or tight end or safety, would anybody take the same kind of notice? Doubtful. There are lots of strong Christians playing in the NFL, but QB is easily the most visible position, where the drama is concentrated. So again it's a confluence of things.
[Edit: I forgot to add a 4th element for Tebow: he's a QB who likes to run over people when given the chance and who prefers to run north/south.....both of which are EXTREEEEEMLY rare in today's pro game. This is actually notable enough on it's own for fans like me to make him eminently watchable. As I told DC in a thread not long ago, this is the reason I root for the guy.]