AFAIK Huge wind turbines have electric machines tuned to the speed of the turbines, so they don't need high ratio gearing.  

The huge ones have a planetary transmission that brings the slow 30-120rpm to the relatively noisy 'efficient' turbine speeds.  those low speeds are not awesome usable for major power generation.  As total power goes up, the efficiency of the transmission goes up (to an extent) - and it goes up significantly going from 'very small' to 'very large' turbine.

Speed doesn't usually matter for power output, if you have the torque.  You can use multiple-pole machines. Hydro-electric alternators might only run at 600 RPM (10Hz), but give 60Hz out.

Agreed about the point of making the correct frequency - but thats not a concern for these guys; its about getting the generator to its most efficient running mode - since you could run a low strength generator at infinite speed or a very (imagine infinitely big) very large generator extremely slow (.1 hz) and get the same amount of power, but its not feasible due to our friend friction.  Yes power frequency is a huge part of it, and engineering in the preferred domain of usable values is a good thing to plan ahead about - there is still an ideal for every generator.  
I'm not sure if I'm phrasing what I mean properly - what I mean is 'good point'. :)

They can use car axles as the support, and the disk/drum brakes as the magnetic rotor and a fixed coil stator...

There are lots of options.

www.instructables.com/id/Turbines/

wind turbines guide...