Yesterday, Technorati responded to my inquiry:

I've taken a look at the issue regarding picking up your pings for "www.pingv.com" and "blogher.org". After making a small adjustment, I've sent our spiders to revisit your pages and your blogs have been indexed with your most recent posts.

This leads me to believe that perhaps their spiders were not optimized for these sites. Whether that's related to Drupal or not, I don't know. I appreciate their timely response. (Marianne Rchmond has praise for Janice Myint, who was the rapid responder to my trouble ticket as well. Thanks, Janice!)

All of our Drupal-powered sites (including BlogHer, pingVIsion and this humble blog) seem to be tracking properly on Technorati now.