I received an email about this topic and have not read the whole thread, so forgive me if some of what I write is redundant.
To the OP, as some have mentioned, 4.5 hour rounds in the U.S. tends to be the norm.
As far as pace issues, my thoughts are these:
It can start with tee time spacing. A few courses even have two spots every 15 minutes (always about the money). This will always cause a logjam and later tee times will be delayed. Another poster mentioned that more difficult courses need more spacing and I agree. This is something the course should regularly monitor.
Ranger/ marshal enforcement. This seems to be sorely lacking. When was the last time anyone saw or heard of a group being removed due to slow play? If those players get pissed and vow not to come back, the course needn't worry about them ever again!
Players unaware of the etiquette that includes allowing others to play through.
People searching for lost balls and fishing for ball in lakes every hole. Ugh!
Finally, some have needless routines. People watch the pros and emulate them, sometimes doing things like plumb-bobbing or using aimpoint when they haven't a clue what they're doing. Or, taking fifteen practice swings because, well, that's how Tiger did it.