Birthday parties at my house are laaaaame. It usually consists of the bastard Auntie coming over, who I don't like too much. Then, my sister and her army of kids come around as well, and I don't get on too well with her these days.
Parties and going out with friends for your birthday however is so much better.
As for anniversaries, as the Ine says, it's definitely to sort something out, as our anniversary falls on September 9th. So, I'm working that day and she's been back at Uni for then. We've also not celebrated my birthday together, in the time we've been together, again due to it being in January.
Basically, if our anniversary was in Summer, or December, it would be easier to celebrate.