Bob,
There are many reasons why play is often slow in the U.S. and particularly in CA. I doubt that putting out and scorekeeping for handicap purposes are in the top three or four.
I confess that I am of the pencil and card type, normally making copious notes while playing, and occasionally clicking (discreetly) my digital camera 10, 20, or 50+ times. I've been known to do all this while shooting a decent score and finishing in a foursome under four hours.
I believe that density (amount of play), culture, and course characteristics are far more important contributors to slow play. Public courses that run 100,000 rounds per year will be slow. In SoCal, unless you play in the first few groups, you're out there for five to six hours.
Culture is a broad category which includes types of golfers who play socially within large groups without much concern to those outside. There are many golfers who simply enjoy chatting, observing everyone's shot, and are seldom ready to hit when it is their turn. I think that going with purpose to your ball, being ready, and hitting promptly when it is your turn is the key to a good pace of play. The culture can be changed more easily at private courses. Saint Andrews seems to have accomplished it with a hard-ass, no nonesense mobile marshalling group, but I doubt that this approach is transferable but to a few other public venues.
Finally, long courses with considerable distances between tees and greens (modern gca); extensive natives, rough, "trash"; many bunkers, creeks, lateral water hazards; and heavily contoured, fast greens make the four hour round impossible.
Like many, I am guilty sometimes of playing to the speed (and level) of my group. This is also a tendency within groups on the course (playing to the speed of the group in front of you). Personally, I hate having people waiting for me, so, when things are slow and people are pushing me, I get anxious and testy. In this regard, I think I am in a small minority.