You misunderstand. This developer is targeting the IEMs that come with the Vive for their audio tuning, over the ears in this game may cause a problem. If the game was tuned for over the ear type of headphones then IEMs would cause problems. The benefit of the Rift is that everyone will have the same decent quality headphones and the positional audio in every game will be tuned for that one set of hardware.
That's a huge plus.
Now if every Vive came with the same high quality over the ear cans, the Vive would beat out the rift in the audio department, but there is a lot to be said for everyone having the same exact headphones.
Audio designers generally tune for whatever the most common setup is. They can do better if they know everyone will have a uniform output.
I understood just fine. I think a lot of people are overestimating the difficulty of positional audio. The Division does a fantastic job of it and it has no idea what brand or style of headphone I have.
Yes, it is an advantage for the entire audio stack to be a known quantity. However, since they don't know the shape of the end user's ear, it is still somewhat of a guess.
The convenience factor of rift's built in headphones is far more compelling than any alleged sound advantage. Of all the rift/vive comparisons I've read, I don't think anyone has declared one or the other to have superior positional audio, but most have mentioned that vive is more cumbersome because you need to use separate headphones.
The developer everyone loves to quote lately said this:
"That's technically still true for the Vive but the fact that they're IEMs will stop many people from using them. At least that's what happened in our office. Out of 10+ people here only one can actually stand IEMs and that's me. "
Why would they target IEMs if nobody is going to use them?