Shivas,
IMHO, preshot routines, even something like Sergio's painful display, doesn't slow play very much by comparison to not playing ready golf. I think this is why cart golfers are so slow. When I'm walking, I'll walk up to my ball wherever possible and be figuring out the yardage, the club I want, the wind, etc. while others are playing. When it is my turn I just have to stand behind the ball to get my line, take a sort of half practice swing, address the ball and go. When I'm forced to take a cart, I'll walk over to my ball while my cart-mate is taking care of his shot. Unless I have no clue how far I might be, I'll bring the club I think I need and one on either side, which will cover me over 90% of the time.
Cart golfers usually are loathe to walk any further than the direct line the 90 degree rule requires so one guy sits on his fat ass in the cart and watches his buddy, waits for his buddy to replace his divot (we hope) wipe off his club, put it back in his bag and get back into the cart. Only then to do they move on to his ball and the whole process starts over for the other guy. Sometimes you see both carts do this together to four balls in turn so they can all be jawing away the whole time. They view a round of golf as a social experience so it doesn't matter to them how long a round of golf takes, and don't understand why anyone would worry if a round takes 5 hours. Hence the American expression "day of golf". When Scots say that they are talking about 36 holes or more!
The Sergio like guy with the slow preshot routine isn't the problem, it is his buddies all standing their slack jawed while he does it. Pros aren't the best example of speed, but while Sergio is doing that, Tiger is busy figuring out his shot. He doesn't wait until Sergio's ball is done rolling before he asks his caddy for the yardage, examines his lie, etc.