Really? My experience is that they generally get their on time for weekend games, both day and night. It's the weekday games where I notice late arrivals - the yuppies have to get off work.
I don't know, maybe it is just my experience. But, I usually get to games as soon as the gates open to watch all the players warm up and hopefully some BP. It always seems like the place seems completely empty until a few innings pass, then it is just almost empty.