No, it's because ...
1) Last year we used USB dongles and it was a bit of an operational nightmare. The drivers kept conflicting and we had to rebuild the laptops a few times, Windows would freak out from time to time for no apparent reason, the tests all had to be initiated by hand, and there are differences in USB dongle performance anyway so it doesn't totally insulate you against that.
2) Last year I got a lot of criticism around "who uses USB dongles? Everybody's on smartphones!" ... so I thought we'd use those popular smartphone devices. I tried to make the devices as similar as possible.
3) Sensorly was willing to work with us to create a great field test app that I think tested a bunch of connectivity aspects really wekk.