I think part of this transition is Apple subtly suggesting that people don't need to have their laptops plugged in as a default any longer. The Magsafe is so easy to attach, most people I know have one in their usual work spot and just snap it on every time they sit down there, even if it's just for 10 minutes to check email. The comparative inconvenience of the USB connector means they will likely be a little more intentional about plugging it in...but the incredible battery life of these devices now means you really don't need to. There's no need to snake a power cable to your table at the coffee shop when your laptop gets 10+ hours of battery life. You don't even need to plug it in on your desk at home, or working in your bed, on the couch...if you're just plugging it in on a side table when you close it up for the night now, the whole tripping hazard becomes a pretty moot point.
Edit: ah, I see jakobegger has beat me to this comment below ;)