I am not an expert on the subject, but I also think he is misguided here.

In the Western world, where we read from left to right and top-down, we also expect our UIs to follow that order: first you type something and then you click on a button. Also I don't know if these visual fixations are really relevant here. Power users will use the enter key, so for them it's the best, anyway, if the button gets out of the way. Computer novices, on the other hand, will look away from the screen at the keyboard, while typing.

Even Google places the search button at the right of the input bar. I am sure they have A/B tested every possible variation and this turned out to work best. Last but not least it's simply what we are accustomed to.