Actually 1.1 is going to indirectly nerf Regulus, by capping the move speed reduction. He has no interrupt, and no stun (deadeye is shit and doesnt count) but he has 2 giant slows in mines and motb, and also maim as a minor slow. Someone mentioned a while ago there is a hard % cap at the amount of slow you can stack on, but the new patch is adding a movespeed figure to that as well, so no more practically static enemies to throw mines under 
More pressingly, and perhaps a big factor in the DG ranks, is that Reg is a very strong auto attack late game monster. UB is identical, so you can consider any game going late on to be dominated by these two. Why is this important? Because if the community skill level is on average not high enough to close games out quickly (under 20 - 25 minutes) these two are going to run everyone into the ground and win with their +attack speed and +crit items.
Why do the assassins have better win ratios? Because they're a lot easier to play with some degree of competance. Minion micro is difficult at times, to be really effective you need to keep track of when your priests are going to heal you, and of course where all your minions are at any point in time, as well as anything your DG is doing. This is a lot harder than casting MotB and then throwing mines once they cast something, but its also much easier to push a lane by yourself as a general. All the generals have far more staying power than the assassins...try pushing an Oak/Sedna team out of a lane with ANY assassin combination.
