I'm wondering how this piece of n00bishness is at the very top in HN.

The only reason there is a perceivable diference (in the presence of patterns) is that rand() is not very solid (it's optimised for speed, they recommend mt_rand() where a stronger generator is needed, and you can still do much better).

PHP's mt_srand is a Mersenne Twister, which is pretty good http://en.wikipedia.org/wiki/Mersenne_twister