I don't think you are being unreasonable, and I can totally understand how you feel. Up until my DS married, my DD always had to remind her brother when it was my (or DH's) birthday/mother's day, but now he's left home, and lives in another country, I honestly wouldn't be surprised if he totally forot! He usually gets flowers delivered me, again, not much thought gone into it, but at least he's remembered, so I'm happy with that!
I know not all sons are the same, but from what I hear from friends, this seems to be the norm amongst many. My daughter, on the other hand, who also lives in a different country to me, is one of the most thoughtful people I know, and would never dream of forgetting anyone's birthday/mother's day/father's day.
Right from when I was a young child back in the 60s, into my teens, 20's, and after I married, I would always remember cards & gifts for both my parents, and grandparents. I can only think that 30/40/50 years ago, we had more simple lives, and these days young couples seem so busy with everything from their family/home lives, to their working lives, that perhaps they simply do forget?! Or, I don't mean to generalize here, but is it a 'man thing'?
Personally, I'd try not to let it upset you too much. He did, at least, remember your birthday.