Somebody asked Chris Sacca (one of Google's main acquisition guys) this at the first Startup School. His answer was "Build it in whatever language will let you get to market and start getting users fastest. Usually when Google buys a company, we have to rewrite all the code anyway to take advantage of Google's infrastructure and scale to millions of users."
This doesn't answer your question about Zenter, but it should about Google...
I think you are right. Whois.sc cached the server response headers before Google switched the server, and it was "Apache/2.2.4 (Unix) DAV/2 mod_jk/1.2.21 SVN/1.4.4". mod_jk is a Tomcat connector, so it would make sense that the site would be written in Java.
