It's probably just a personal thing. I'm in Europe and always take my birthday off - I don't understand why anybody would want to work on their birthday. Even if I don't have plans to celebrate until the weekend the idea of working on my birthday is very depressing (in fact in rarely celebrate my birthday and if I do it's something small like dinner with a couple of friends). To be honest I thought it would be more prevalent in Europe given we seem to get more time off and taking time off is less 'frowned upon' (at least this is my experience compared with my US based colleagues).