I do not think the statement is meant teasingly -- Holmes is extremely proud of his store of knowledge and never misses a chance to show off. It would be very out of character for him to pretend to an almost-stranger (the two are roommates at that point, but not well acquainted) that he lacked a basic point of fundamental knowledge.
The idea that the knowledge would not be useful for detecting is quite startling. Heliocentrism makes a VERY large difference in how one views the travel of stars and planets across the night sky, and it is "little" details like this that usually make or break a Sherlock Holmes case.
I rather disliked the modern movies for making Irene Adler a romantic interest. I think it's very clear from the books that Holmes is very likely asexual. Certainly, he is misogynistic -- he never misses a moment to expound upon how women are not trustworthy or worthwhile, and he frequently (in the books) fails to provide valuable information to his female clients because he assumes they can't handle the truth. Rather annoying, that, since he has no qualms about still being PAID.
