Hello Jim,
I see XML as the modern equivalent of the fax; you can have any brand of fax you like, as long as it follows the handshake/comms specification. So you can't be captured by a vendor unless you allow the vendor to tie something proprietary into your faxing system.
I think xml will also mirror the evolution of the fax; when faxes first appeared, customers had to pay $15 to get a fax bureau to send a fax across the country, but eventually faxing became a commodity and fax bureaus either developed new services or closed.
Regards
JR
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1