People seem a bit confused about recovery drinks. As I understand it, when you ride or train hard, you rip through the glycogen reserves in your muscles and liver fast. There's a window – duration uncertain, generally quoted at 20 minutes-30 minutes after you stop when your body is basically screaming for carbs and absorbs them faster. Miss that window and it takes considerably longer to top up your glycogen again and you need those reserves for efficient metabolism when riding.
The protein element in recovery drinks is because research shows that a mix of protein and carbohydrate leads to the carbo being absorbed more quickly during that glycogen refuelling window, it's not that you need big chunks of protein to rebuild muscle at this point, just that it means you absorb the carbohydrate more rapidly.
Chocolate milk shake type things have around the right balance of carbohydrate and protein, so work as well on the carbo absorption side of things as specialist recovery drinks. The latter have extra minerals etc that you might need, but you can get these elsewhere.
And that, as I understand it, is about it. In simple terms, bang some chocolate milk down within the 20-minute glycogen window after you stop exercising and your glycogen levels return to normal faster, so your recovery is better. Logically the harder your ride and the more trashed you are, the more beneficial some sort of recovery nutrition is going to be.
That's how I understand it to work anyway. There's other stuff around like the Ribose that Torq seems very keen on, but god only knows whether and how it works. Sports nutrition seems a tad band-wagonesque and it's hard to filter out the chaff.