Some validation errors ARE a result of standards changing and/or browser support differences -- and those are no big deal (though they sometimes illuminate browser inconsistencies), but some of the errors on your site are coding errors -- like I said, unclosed tags or elements in "illegal" places and those are not that hard to fix and it's important to fix them. Some may be causing the problems you are trying to fix -- so you are wasting your time trying to fix them if the errors are still there.
And yes, you are right many themes do have errors, although I believe that the ones on the WP theme repository MUST validate before being accepted. "Premium" does not necessarily mean clean coding...especially as versions and standards change.
BTW, if that's a commercial theme -- you really should look to elegant themes for support -- that's part of what you paid for.