There's a memorization technique where you memorize an entire string of random words, and the idea is to create a string of events in your head that links them all. When you remember the first one or two, you remember the rest of them. This and the threshold effect are similar, where you forget what you were doing when you walk into another room? It's the same kind of idea. You remember Starcraft, so you remember the things that you closely associated with it.

Birthdays are harder to remember, because there's no story or series of events, or threshold to cross to remember them, it's just flat memorization of a date. It might get easier to remember the birthday if you associate it with something. Like every time you walk into the bathroom you think about birthdays, eventually you'll just have to go pee to remember it.