Over in comments Phil Ringnalda notes that Google now seems to be indexing this stuff after I made the dasBlog config change.
Certainly seems to have. It's not actually that G doesn't index pages with query strings, so much as that it doesn't like to risk long query string values when the variable name includes "id", because that smells like a session id. If rather than ?guid= dasBlog used ?whatever=bunchacrap then Google would be fine with it.
This explains why google was indexing permalink.aspx?guid=250 (the old radio content imported into dasBlog) but not the new content put into dasBlog. Phil doesn't like the stupidly long GUIDs - nor do I. Since dasBlog keeps a post count, I can't see why they didn't go for a much simpler id - other than the risk of duplicates when the software fails!
I'm tempted to change the web site to use permalink.aspx?article=ssssssss rather than ?guid= to see if Phil is right - but it is most likely that he will be so I can't be bothered 