The debate about higher rankings has been going for many years although I personally do believe that having a website designed to W3C standards does help rankings in many ways. Also producing a site that is CSS and Layer design helps too because you can decide more where the things that matter to search engines are positioned in the code while being able to greatly manipulate the page layout for visual effect at user end.
I read a long while ago that bad code can kill off your site and this was the example given:
Lets say your first paragraph is written for the search engines but you have made this simple mistake -
<p This is the text from my first paragraph and I have written it for search engines while keeping it still readable to humans and good to read</p>
Notice I have accidentally not closed the start tag for the <p>
According to the article i read, the search engines will not be able to read the content as it is supposed to be and will be interpreted as being part of the tag and therefore ignored. this is obviously a really bad thing. So with this in mind, this very basic mistake can be fixed by validating the html.
Simple yet it just goes to show what a little time and validation can do for a page.
I don't think, that this is so proofed. First: Google relies much more on incoming links. W3C and also - of course - Wikipedia have LOT of high qualitiy backlinks. So for a real comparison content and links should be quite the same. But that's difficult. Second: Google crawls non-semantic-code-sides also quite good. There rank also bad (coded) sites very well (newspapers, ...). So in my optinion W3Csites are the best starting point, but no more.
If your website is W3C validated then posibility of scoring high rankings on search engines but alongwith this many other facts are also in consideration like - Informative & effective Content, Backlinks with relevant websites, link popularity and timely updation.