Actually, Blue is right about that, about clocks with roman numerals having IIII instead of IV. It's traditional, and the common explanation I've heard is that it has to do with making the clockface look more balanced. Not to say that I completely understand it, but there you go (and this isn't unique to the US, but has been traditional with clocks for quite a while).

The Straight Dope even covered this topic, it seems, if you're interested: http://www.straightdope.com/classics/a2_153.html

Reading through all of the letters Cecil got on that subject, you can see there's a lot of debate about the WHY.... but there's no question that it has been that way for a very long time, and Blue's original point was correct.

One especially interesting point that is brought up there is that the IV rendering of the number 4 is actually more modern..... someone who knows more could verify it, but it also does perhaps at least partially explain why that tradition started, and why it kept up from there.
This comment was edited on Aug 11, 20:49.