Whilst developing top spec websites to tight deadlines, html validation sometimes takes a seat further back than it probably should.
Due to modern browsers becoming more forgiving, front end users probably will never notice that you spent half an hour tracking down that rogue image without an alt tag or a cheeky div inside a li just to get a green box on the w3c compliancy test.
Nevertheless, standards are always good to work towards and at Senior we always strive towards keeping our code as clean and tidy as possible.
Building compliancy into a content management system adds a whole other layer of complexity as users can’t be relied upon to maintain standards themselves.
We have recently made many improvements to the River CMS code and our own site now passes the compliancy test as do many of our clients. The only code that can’t really be optimised is third party sections such as the google map code on the contact page (A quick search revealed that this is an almost impossible task!). Switching to theTinyMCE editor has also meant that the code entered by users is on the whole fairly accessible without any interaction from us.
Is w3c compliancy still important? Yes, of course standards are still important, however it needs to be a balance between the cost of time spent and the added value it will bring to the end user that have to be the deciding factor.
For further reading on this subject I can point you to here and an article that speaks a lot of sense here.