_In advance_ means "ahead in time." _Thanks in advance_ means you are thanking (people who answer) before you get any answers. It doesn't seem to be rude, and it doesn't seem to imply that you are not going to read the answers given for your questions.

That said, normally on SE sites it's preferred if the question just contains the question being asked, and not phrases similar to "any help is appreciated," or "thank you for reading me."  
Such phrases, even if they are an extra, are surely less noisy of any phrases added before the question itself, such as "Hello guys," or "Hello Drupalers," or "Ave, conncetioniorum virtualorum habitantes!" That is probably the reason why the greetings in a question have been removed before the thanks, which (as far as I know) are not yet automatically removed.