the google white paper at http://infolab.stanford.edu/~backrub/google.html declares that google's crawler started off in Python (which is probably higher performance than Java) but anything requiring best performance is written in C and C++.

So Java, which inflicts a foreign virtual machine architecture on every execution, carries the risk that it cannot take advantage of procedural programming compiled into native machine code where a high throughput algorithm demands it.

Perl on the other hand is implemented in C and can even call C routines if really necessary, while any object-oriented needs it can take care of itself.

So given that Google is a tried and tested approach, it seems to make sense to use the languages most able to follow in Google's footsteps, albeit using C where necessary, i.e. Perl and C.