Whole food or liquid, it's still just amino acids in the blood stream. I haven't seen data comparing the glucagon responses to different amino acid profiles in athletes, though.
Consumed liquids are released from the stomach more quickly than solids, though.
Drinking whey would still be fast compared to say, eating a solid chicken breast. And the way casein clots, I've got to think that it'd release its amino acids more slowly into the circulation. Plus, the functional food aspects of whey are also cool - increased glutathione, etc., so combined with the convenience of powders and the hydration provided, I still think (whey-containing) protein drinks have their place peri-workout.