You won't ever see a pro mixing or mastering on a pair of headphones. The ear simply doesn't hear things in isolation, and artificial techniques to emulate different speakers is simple marketing hype. This is right up there with mike simulation software... you remember, the promise that you can make one mike sound like a much better one by using software. Hype.

You use headphones to check detail, especially if you can't get absolute silence in your listening environment. You might get a pro to say he mixes on them, but trust me... he's doing it for money (or free gear!). When in the studio, those nearfields and midfields are what he's listening to 99% of the time.