Code that is valid is code that is correct. Whilst unvalidated code may run as intended on the computers it was tested on, developers have no way of being sure it will work correctly on other computers. Producing W3C compliant code ensures the site will work for everyone.
The global organisation that manages web standards (W3C - World Wide Web Consortium) provides a service that checks your web site to ensure the code is 100% correct.
Yes. All sites that SWEEB makes are fully validated. Before we release a web site, we have every page checked by the W3C to ensure that both the XHTML and CSS (the core languages of web sites) are 100% correct.
The symbols at the bottom of this page on this site are certifications that our web site has been perfectly built. Every site we build earns these.