I don't know if it's a cultural legacy. Most engineering heavy firms where people are allowed to set their own hours have people roll in between 10 and 11. I don't think I've ever been to a tech company where the majority of people are in by 9 unless they have to.

I think plenty of programmers tend to be natural night owls and it's not uncommon for them to be working at 3am out of their own preference.