When Annie Met Sally

I'm just watching "When Harry Met Sally" on Comedy Central. and I've only just realised that the reason that I like it so much is because there are loads of bits taken straight from Woody Allen's "Annie Hall" and "Play It Again Sam". The references to Casablanca, The split screen phone conversations and the back story that men and women can't be friends because the sex part gets in the way. And even the theme song is the same as in Annie Hall ("It Had to Be You" - It's an instrumental in When Harry Met Sally and in Annie Hall Diane Keaton sings it. It's also on the soundtrack of Casablanca) In a couple of scenes in WHMS Sally dresses like Annie. Even the credits are straight from a Woody Allen Film, plain white text on black. There are probably another hundred or so references, in there, that I haven't mentioned.
I'm not saying it's a rip off, it's definitely a homage. It's one of my favourite films but for some reason I've never realised this before. What's been going on in my head for the past 20-odd years?