I haven't tried hydro yet ~ but I only hear good things, that if done right the plants do better. Out of my 4 (all soil), one plant developed resin and frosty goodness more than a week ahead of the others. Actually, its the one that got the CFL reinforcements.
I would suspect that your hydro plant has had more available nutrients and oxygen in the roots accounting for the better development.
Yes the yellowing and leaf drop are normal. I am having the same on two of my plants. However one of them is looking almost sick, so I had to devise a course of action. First, I flushed all the plants last night in case of fertilizer buildup. Today I gave them all a mild foliar feeding of 15-30-15 at the end of the dark cycle in order to be sure the leaves were wet when the stomata were open. It's only been a matter of hours but I beleive I see an improvement. I also got a pH meter today. Post-flushing, all the plants are reading slightly alkaline, pH for two plants is 7 and the other two are 7.5 - so I believe that at the next watering I will be able to put a normal dose of fertilizer to the roots, as well as giving another mild foliar.
Hopefully this will give the nugs a decent shot in the arm before they start ripening.