James Duncan Davidson has a nice article on his choice to use XML for Ant scripts:
http://x180.net/Articles/Java/AntAndXML.html
His comment that "I never intended for the file format to become a scripting language" and "If I knew then what I knew now, I would have tried using a real scripting language" reinforced the argument I've made with friends and colleagues for years that you almost always end up needing a full-blown language in the end so you are much better off just starting with something like Python rather than inventing a domain-specific language.
I've seen a similar argument made (and myself made it) as a counter-counter argument against Tcl: Anti-Tcl says "Tcl isn't a full-blown language". Pro-Tcl says "Tcl isn't intended to be; it's for the little jobs that don't need a full-blown language". Anti-Tcl counters with "but what starts out as a little job almost always grows to a bigger one". I've used that argument against Perl too.
I'm wondering if the notion "you almost always end up needing a full-blown language in the end so you are much better off just starting with an existing full-blown language rather than using a little language or inventing a domain-specific one" has a name? Has someone claimed it as their Law yet?