I don't know of the other side of the World, but in this side of the World, men are responsible for every financial responses in both marriage and the boy/girlfriends relationships.
The demands of financial expenses is being too much at the men sides.
Who made it that way and what society is that, if I may ask? Culture is made for the benefit of mankind and as such any culture that becomes antagonistic should be stopped. Yes, stopped. I believe there are enough exposed and learned folks in your society, they should see the need to weigh in and reveal that obnoxious part of your culture. Women are supposed to be helpmate and partners in progress, especially when in a relationship or married.
On the other side of the $50 story, I think your friend wasn't emotionally commited to his relationship. How else wouldn't he have had an idea what's top priority on his girl's worries rather than giving her that cash because he wasn't sure. Anyway, I don't even know what those who celebrate Valentine's Day benefit from that. I don't see any need for it because love is supposed to be an everyday thing, not a once in a year thing.