Lugia actually has some pretty hard counters, believe it or not. Lileep is by far the best, due to suction cups. It also has worry seed to prevent lugia from sleep stalling. However, he needs rest if he wants to win the toxic stalling war.
Oddly enough Lileep+Evo Stone+Sandstorm boost can tank an attacking Lugia's hits very very easily (even critical hit Aeroblasts unless they've got 4+Calm Minds to back it up) but really, how often are you going to see a Lileep in OU? 'Tis possible and some people love to specialize in the UU and Underevolved pokes but on the whole, I doubt Lileep is going to be widespread or going to remotely come close to being a reason for Lugia to come down to OU. Lugia with Toxic destroys that Lileep (unless it Rests but then Lileep is bait for anything else to come in) and it can carry Safe Guard or Substitute over Rest/Sleep Talk (and stop Lileep from doing anything since the only way it can really attack is through Toxic). Lugia will more likely PP war stall you then and Lileep while able to take on the attacking variants, can't really do anything to it besides Toxic (which any poke can Toxic). And like Quagsire, Gastrodon, and Ludicolo being good counters to Kyogre does not make Kyogre OU, so does...Lileep and the other very few things that actually can do something to Lugia. Which really isn't much.
And Chansey/Blissey are much less common than they used to be, especially Blissey which used to be a staple in Gen 4 (and pretty close to is in Uber if you're not carrying something else) but is only on a few teams in Gen 5 and again, Lugia can pp war stall Blissey/Chansey via Rest/Sleep Talk, Substitute, or Safeguard. They can't do anything to Lugia.