I do know about that, however, that doesn't really answer the real issue, i.e., that I want the one tap dialog box. If there is no solution to bring back the older functionality then I'll settle for holding it down.
Glad I found this thread, I thought there was something wrong with my MBA after upgrading to Mavericks; like a setting for the power button got reset. I am with you, I wish there was a one-press option to bring up the dialog box. Anybody want to do some digging to see if there's a "defaults write" to change this behavior?
So, it turns out that there's an easy but annoyingly not obvious solution. If you quickly press the power button, your laptop sleeps. If you hold down the power button for about 1 second, it brings up the good old dialog box. It's actually a pretty good middle ground once you get used to it. Hope that helps.