Doesn't the Wii let you postpone firmware updates unless you're trying to play a game/app that demands firmware version X?

And iirc they shipped the upgrade on their tent pole first-party games so even if you didn't have your wii hooked up to the internet you could still take advantage of the updates.

Yes. I don't think I have ever been required to install an update, with the exception of the one a couple years ago when Nintendo EOLed some of the default channels.

I seem to remember that it downloaded (and maybe installed) some of these while the box was in standby mode, so rarely did I have to install one while waiting to play.

Well I certainly didn't say that. But they were less frequent than the PS3 and generally much smaller/faster.