I'm on your side on this issue. We've done some XML with other companies (ok, you made me say it, B2B... eewww... a buzzword) and never have we seen a DTD. We never even see standards on XML docs from the same comanpany. One XML form may have ShipAddress as a tag, and then another on may have ShipToAddress.
So, I still think Mikes original question stands. If the data is...
and the DTD says it's 3 numeric, is the value 999 or 99999999, or is it invalid data? What if it's
<quantity value="999999999/> or something even wacky-er.
I think that because of XML, bandaids were made up such as DTDs and Schemas to fix these types of problems, but because it's such a simplistic idea it just made things worse. The need for some pretty sophisticated (bordering on AI) is needed for this "simple" form of data transfer.
XML was never meant to replace X.12 or be used for EDI, but some brilliant person who's never done EDI probably saw it and said "Hey, I can read that. I can't read X.12, so this must be a better EDI format."
XML used for web pages is a good idea, but EDI, no.