I also have a maxed 11", 1.6/4/128 and it does NOT play Netflix with HD enabled. It stutters big time if there's much movement in the scene. I don't understand how it could possibly work for you. Are you really running HD or just HD enabled?
This is how it is for me too, and I also have the ultimate Air.
Netflix HD plays back better in Safari than Chrome, but it still stutters badly during scenes with much movement. If I turn off HD, it is silky smooth.