@ Steven Bradley:
1. "It doesn't need to validate if it works..." Nice attitude. BTW, I've read the article, but using invalid code sounds like:"Google doesn't need to validate because most of the websites are invalid". Surely, plugins from invalid sites will make your code invalid.

2.I suppose that most of errors of this web come from Google, and you are right that I didn't check where they come from. Apologises for this one.

3. I agree with this point. Usually, fixing one error reveals more of them. Naturally, the website code error is not one line problem but the concept error. Why not chase and stamp them out?

4. Alright, social networks, Google plugins (or any invalid site plugins) will usually increase the number of errors but improve SEO.

Note: Why the hell can't the internet be flawless, valid and nice?

I didn't mean any insult, it's just - how often do you see valid website? And why it can't happen more often