Presently, there are numerous web sites which have invalid code but still do work fine gratefully because of the latest web browsers that automatically correct most of the minor errors in the bad code . It can be said that it is not required for the code to be perfect however it should also not have well formed erroneousnesses which will can damage the original performance of the web site.
Since it still makes sense in having a list of web sites with bad code which can be refined by the browsers that have got recognising the latest html adaptation though not entirely but just quantity enough to adjust specific tiny things in the code . These minute defects in the code can be mostly because of the different html editors used by the users and also the hand coding done by them.
If there is serious things which lead to drastic errors in the functioning of a web site, then Google would be sure to notice it and point to the users . If Google really considers even the minor code faults then it can be said that there would be lot of web sites which can be left behind. Only because the search engine understands what the page is all about hence it does not consider the well formed errors .
Google is capable of understanding and dealing with the pages that are grammatically correct even though there are minor errors in the page, it also can different between casual pages and useful ones which happens to be the main reason that there are still a big listing of web pages exposed by the search engine even if their code has minor faults.