This was just posted at the Google Mobile Help forum to a question I posted:
Thom (Google Employee) says this answers the question:
Hi all,
The BlackBerry Storm uses a highly-customized GUI, which prevents Google Maps for mobile from being viewed in landscape mode. We're still working to integrate the app with this device, and we haven't yet put out a new release since the Storm has launched. I reallize you're all eager to use your internal GPS with Google Maps for mobile - and we're working to get an update soon. I can't give you a timeline as of today, but I'll update this group when I can give a more accurate picture.