Heh... yeah, like I said, I was so deadset on keeping that movement measurement that I never even bothered to look up what 5E actually did. I guess the 5E designers agreed that the alternating 5'/10' was unnecessary.
Funny, I am the opposite. I never bothered to check, b/c I can't imagine it not costing (in my group's language) 1.5 boxes of movement to move diagonally.
EDIT: That is to say, I find the language of "alternating" confusing and prefer measuring distances in boxes anyway. So 1 box horizontal, 1.5 boxes diagonal is nice and easy to remember.