Note that you could make a wind sensor also without an encoder, you can use the "hot wire" principle and save a lot of money.
Wrong. A hot wire sensor has several subtle drawbacks and is not suitable for measurement of wind speeds in a fixed outdoor location. Although very simple in principle, there is a complex relationship between air speed and the sensor's output. There is also the issue of the effect of rain and snow on the instrument.
Sorry, the linear relationship between a cup anemometer's rotational speed and wind speed, the inherent averaging effect of the rotational inertia of the vane, plus the dirt-simple direct interfacing of the instrument to a microcontroller's digital port still makes it the top choice for amature wind speed measurement.