Real world RNGs get randomness from two sources: (1) the timings of random events on the machine (primarily network traffic), or (2) a hardware device that runs several oscillators on different clocks and detects coincidence in the derived square waves. Even #1 alone is normally sufficient in the real world. While you're right that there are attacks against RNGs, it's never going to be because an attacker gets control of every little bit of stray RF in your data center such that he can control the exact timing of packet arrival, packet retransmits, etc.