What is a wireless crankset? For example this (rather expensive) item: http://www.wiggle.co.uk/sram-srm-powermeter-pro-wireless-bb30-double-chainset/

What is actually wireless about it? Is this for a cadence meter? Wireless shifting?
The crankset is not wireless, the power meter inside the crankset is wireless, the power meter inside measures your power output and wirelessly transmits the data to a head unit for display near or on your handlebars.