Personally, I don't know enough to know why China hasn't invaded Taiwan. I don't know that much about military deployments or about what kind of things the Chinese government fears. But basic logic tells me you'd have to come up with a good reason why China is deterred from doing something it has clearly stated it wants to do ("liberate" Taiwan) if you assert that American might is not the reason.
Dan's comment was a throwaway in a much longer post mostly not about China, so he probably means that American military pressure has only certain effects on China. Presumably China can get away with a lot without fear of any US action, but knows where the lines in the sand (or sea) are drawn.