I think I found the problem.  Due to the change in the user agent string for IE11, ASP.NET is not recognizing it as a browser that supports Javascript.  (Maybe if Microsoft had more company-wide picnics, the folks from different departments would talk to each other more...  :-)

See  http://blogs.msdn.com/b/ieinternals/archive/2013/09/21/internet-explorer-11-user-agent-string-ua-string-sniffing-compatibility-with-gecko-webkit.aspx

I can’t seem to find a version of this hotfix for .NET 4.5, though.