By using cursor key for voting you dramatically decreased usability, for example I no longer can use Platform Key (Win/Command) key + left arrow to go back to previous page.
Normally I'd agree with you (e.g. I hate Blogspot because they hijack Alt-Left for back also), but in this case I actually liked the arrow keys for voting because they were quick and simple. I voted on probably ~5 screens in just a few seconds and felt really smooth.