Windows Live Writer HTML and WordPress XHTML Posts

I been searching the forums to this Qn. but could not find any

I have been using Windows Live Writer for my website but I have lately discovered that WLW produces some messy HTML code, like certain tags are not close. I read up that WordPress aims to follow XHTML standards. However all the post made with WLW render fine in most browsers, is there something wrong with wordpress that it does not enforce XHTML?

• Should I not be concern about this and just continue doing things as usual?
• or Should I drop using WLW and aim for my future post to be XHTML compliant and validate?
• are there any advantages in making sure that the post are XHTML and validate