This is fairly common when hosting arbitrary sites. The VS debugger picks these up, but they are ignored at runtime. You can see this by running outside the debugger--they won't crash the app, but the site content might not show up in some cases.
Because these won't cause an app crash, they usually don't pose issues for certification. If, however, the web content you're trying to incorporate comes up blank and makes the app look non-functional, then it would fail cert. In such cases the problem is
in the external site and would need to be fixed there.
Kraig
Author,
Programming Windows 8 Apps with HTML, CSS, and JavaScript,
a free ebook from Microsoft Press
Also see
second edition preview