Well, my initial understanding was that instead of attempting to update immediately on start (which is what happens on older OSes), the configured interval (4 hours by default) is sticked to (continuing through the time the machine is off), as if the shutdown didn't happen and the computer was running the whole time (example: the configured interval is 4 hours, you shut down the machine for 3 hours - and then it takes another hour for the check to happen).
That would be OK in my opinion; different from the behavior on older Windows, but not necessarily wrong.
However, if you start the computer after it's been off for a long period, and the whole interval (say 4 hours) just starts at the moment - then it's wrong. I'd say a check for a new update still "happens" right after the machine starts even in that case, but maybe it fails for some reason (network hasn't started yet?) and the interval resets. (But I'm really just speculating at the moment.)