Actually - several of them are. For example:

"Another field study compared interruptions in paired, radically-collocated and traditional, cube-dwelling software development teams, and found that in the former interruptions were greater in number but shorter in duration and more on-task (Chong and Siino 2006)"

This is one of the things I find fascinating. You see the same kind of thing over thirty years as technology changes radically. This makes me think that there's something quite interesting happening in meat-space.

Startup environments are not average, and this must be why companies like Github and 37signals can be successful while having remote workers.

Just to repeat. I am not saying that you cannot be successful being distributed. There are lots of good and sane reasons to be distributed.

I'm saying that there is a bunch of evidence that being co-located is more effective.

Today's homo sapiens brains function the same way as in 2006. Productivity of mental workers responds to disruptions in the same way as in 2006. A large majority of programmers and other people working now in IT are the very same people that were analyzed in 2006.

There are a few more options maybe - but nothing fundamentally different.

For example, a cell phone from today isn't fundamentally different than a cell phone from a decade ago. They're both computers and can be used to make phone calls. But with the cellphone of today, I can have a virtual meeting with anyone from anywhere, face-to-face. That alone is a huge improvement for distributed teams.