The decision for Backbone events vs other events is based on this performance review: http://jsperf.com/events-vs-events2/25
I'm curious, though, why they added an external dependency instead of just inlining a solution. There's a couple of good MIT licenced barebones implementations[1][2] floating around, and it's pretty straightforward to reimplement yourself in an hour or two if you prefer.
[1] https://github.com/Wolfy87/EventEmitter [2] https://github.com/hij1nx/EventEmitter2
:)