Ask HN: Is Bing running on a non-MS stack?

I'll preface this by saying that I make my living as ASP.NET programmer so I'm not trying to slight MS. I'm just curious.

http://toolbar.netcraft.com/site_report?url=http://www.bing.com

Sample microsoft.com HTTP Response Header:

Cache-Control: public Content-Type: text/html; charset=utf-8Content-Encoding: gzip Expires: Thu, 04 Jun 2009 16:56:47 GMT Last-Modified: Thu, 04 Jun 2009 15:24:31 GMT Vary: Accept-Encoding Server: Microsoft-IIS/7.0 X-AspNet-Version: 2.0.50727 X-Powered-By: ASP.NET Date: Thu, 04 Jun 2009 16:46:47 GMT Content-Length: 20017

Sample bing.com HTTP Response Header:

Cache-Control: private, max-age=0 Content-Type: text/html; charset=utf-8 Vary: Accept-Encoding Content-Encoding: gzip Date: Thu, 04 Jun 2009 16:49:51 GMT Content-Length: 9295 Connection: keep-alive