W3C CSS and Markup Validation Service

Question

I just finished my first CSS Web site using PhotoShop, Fireworks, Flash and Dreamweaver.  I did the site from the ground up, the visual way according to some tutorials I found that are uploaded at the Adobe Media Player server.  The site checks out with zero errors using the CSS and Markup W3C Validation Services. The design holds together at http://browsershots.org/ in 75+ different browsers.
Just for fun, I checked out Adobe's, Apple's, Maximum PC's and Tom's Hardware Guide's homepages using W3C's Validation Services.  All of these sites had between 80 and 339 errors per page tested.
Question:
Are these errors reported because of some proprietary coding used on the pages that the W3C Page Validator is not equipped to evaluate?
Or, are these reported errors accurate, because the pages get messed up over time because multitudes of folks are constantly making changes, and introducing errors?

Answer 1

Are these errors reported because of some proprietary coding used on the pages that the W3C Page Validator is not equipped to evaluate?
Or, are these reported errors accurate, because the pages get messed up over time because multitudes of folks are constantly making changes, and introducing errors?
It's a little of both. It's also the result of a cost/benefit analysis by the producing bean counters, I think.  If the page will display OK without taking the extra time to code properly then why do it?  I would also imagine that there is quite a bit of legacy code involved. 
The websites to look at are those of the folks who talk the talk....
My personal ethic and workflow prevent me from taking such a cavalier approach.