Nah, he’s a cock. You can argue about the made up event and commercialism all you want but if his mum would appreciate the sentiment he should make some sort of gesture – it’s not hard (or costly) to bung a card in the post or send a text. If you have strong anti commercial views start with your ‘events’ and ask people not to bother for your birthday/christmas/fathers day celebrations – not bothering for others just looks lazy or uncaring, not sticking it to the man.
Having said that I remember being late to post father’s/mother’s day cards when I was in my 20s so they didn’t get them until the following week and I’ve turned out ok, so maybe there’s a self centred phase some folk go through at that age and it’s nothing personal.
Maybe you need to just ‘forget’ his birthday this year and see if it bothers him or not. It might be he’s wired that way or feeling ignored himself might jolt him into doing the right thing.