There are plenty of people annoyed by "Facebook birthdays" already. Granted, it's not Facebook's fault if people think it's ok to just click on a like button or shoot a three-word comment for someone's birthday, especially someone you haven't talked to in a while, and call it a day.
That said, Facebook is not making it any harder either, it is now highlighting birthday notices on top of the news feed, on the mobile apps and sites.
makes more sense on mobile, you don't a sidebar for birthdays, and the notifications generate plenty of activity so Facebook had to make them more visible on mobile devices.
Of course, the fact that it recently unveiled Facebook Gifts, where people can send actual gifts to their Facebook friends, helped with the decision. In fact, the notifications are now nothing more than links to the Gift shop.