Because 242 isn't always the right answer. Some people may want to know how many to beat the game. Some may want to know how many unique stars with only mario. It is wisest to just answer like I did that way you cover the bases with appropriate information. It is obvious that this player is not far along, so he most definitely has not played as luigi yet. So why confuse him by a simple 242 answer rather than actually being helpful? I think some people just want to give a short answer that makes them feel like they know more than someone rather than being helpful to the person who asked a quesiton. I mean think about it. Which answer would be more helpful if you just bought the game. The answer I gave, or simply saying 242?
You're going to let her go the the grocery store without her wedding ring? It actually is a meat market!--Frank Barone
His question was "how many stars?" the answer is 242 surely?
No, the answer to "How many stars are there in total in Super Mario Galaxy?" is 242. Whereas, as you pointed out, he merely asked "How many stars?" Which, without a qualifier, could mean anything from "How many stars in the first level?" to "How many stars in the entire universe?"
Of course as the question was asked on the Super Mario Galaxy board we can safely assume the question only related to stars in this game but that still leaves the number of possibilities to be quite high.