I think the difference in this case is that we naturally parenthesize the sentences differently: (Count up) to 20. and Describe the events (up to) WWII. Bec

I think the difference in this case is that we naturally parenthesize the sentences differently: (Count up) to 20. and Describe the events (up to) WWII. Because "count up" and "count down" have precedence over "up to" in the linguistic order of operations, so to speak. There's of course no "describe up" or "events up", so "up to" has precedence in the second case.