Remember that XML is a de jure standard, not a de facto one (well, we can pick nits about whether a "recommendation" from the W3C is a "standard" or not, but most Corps see it that way, and there are plans afoot to put XML through the ISO). That's very important to PHBs. And if you prefer de facto standards, well there's always MS Excel ;-)
But yes, if everyone thinks everyone else uses it, everyone does start to use it. That's what happened with Java - Sun spent billions (yes, literally) of dollars selling it via articles and advertising and so on, and they convinced the world that it was the next big thing, and lo and behold, it was the next big thing. The beauty of XML is that everyone else is spending billions promoting it, yet we as Perl hackers get to play in the same ballpark as the MegaCorps, which is nice for a change.