As Standard
I'm sold on the idea of web standards. The continual tirade of rhetoric coming from standards evangelists doesn't help with the business case, though.
Do web sites which don't validate make less money, or inherently make them less usable or accessible? Not necessarily. A few examples:
These are some of the biggest web sites in the world, and are all worth millions, if not billions (with the exception of .net, of course). At some point they've taken a pragmatic look and decided that it was worth sacrificing the holy grail of fully validating code for something else - better support across browsers (CSS is unfortunatly flaky in many browsers, adding a development and testing overhead), ease of maintenance, integration with existing systems and so on.
The assumption that none-validating code is automatically "bad" is as short-sighted as the assumption that standards don't matter at all. As with most things, there's a middle ground and a good web professional will use discretion.