Why doesn't Omega theme have an html5 doctype, even if you are using the html5 template?

What is the point of using the HTML5 starter theme if the resulting doc type isn't HTML5 compliant to begin with? Can I update the omega and alpha html.tpl.php files to have an html doctype and header tags?
I really want to go through and update all the template files to make them have all the html5 tags and doctypes and things that I want. If i modify omega and alpha files, will that cause huge issues, other than the problem there would be with upgrading?

Rebecca