Uh... I always pushed the power button to shut the console off. Unless your talking about while in WiiM... nevermind because I always did that. I think you were just having problems.
Of course you could press the power button to power down the system before. I'm speaking of the ability to hold the power button down for 4 seconds to shut down the system; that was not available until the recent update. If the Wii U locked up previously (be it in Wii U or Wii Mode) you would have to pull the AC plug. Now if it locks up in either mode (as I experienced in Wii U mode per my above example, as well as with Homebrew code dumps in Wii Mode), simply hold the power button down for 4 seconds.