Oh, I sure *was* missing something.  The unit I was trying to configure was a 5324, not a 5224!  On the 5324, "crypto generate key" is a config level command, not an exec level command.  Doh. With the right syntax for a 5324, it works fine.  Not Dell's Problem, mine!
We have a 5234 switch which is currently running 1.x firmware, and a pair of 5224s we use for testing.  I upgraded one of the 5224s to 2.0 firmware and wiped its configuration, in preparation for temporarily swapping it in for the 5324 as we upgrade the 5324. Imagine my surprise to find that I can't actually ssh-manage the switch any more because the "crypto generate key" command appears to have vanished from the 2.x firmware with no notice!  "ip ssh server" in the config file still works, but just prints out the now-useless message advising the admin to use "crypto generate key" to create a host key so SSH will work. I notice the latest 5224 datasheet on the Dell web site still claims SSH management as a feature. We've been strongly considering replacing a number of Cisco switches with 6000-series PowerConnects in the near future and were trying to bring the Dell switches already in our infrastructure up to newer software revs just to be sure there were no new, systemic problems (we've experienced this with other switch vendors in the past, where software quality suddenly goes to heck in a handcart across the product line).  I'd call "SSH removed from firmware without notice" a quality issue for sure, so now we're forced to reconsider the new purchase... ...or am I just missing something?    
"crypto generate key" disappeared from 5224 2.x firmware?