Question: Why is it some employers want to do video calls, such as Skype, for interviews instead of just a phone call? The only reason I can think of is so they know how you look, but what difference does that make?

Answer: 
> 
> Why is it some employers want to do video calls, such as Skype, for
>  interviews instead of just a phone call?
> 
> 
> 

Body language.

You've probably noticed that you have more information conveyed to you when you talk to someone in person, rather than on the phone.

The look on their face, the tilt of their head, the shaking or nodding their head - these all indicate what the person is thinking as much as their words do.

This is what employers are trying to gain (at least to some extent) by using video rather than just phone calls.
Video calls give them a better look at you in a number of different ways. The audio quality is clearer than phones provide. They can check that you're able to dress properly and groom yourself. They can see your body language, and you can see theirs.

On the whole, video calls provide a much better experience and clearer communication between both parties. If both parties have computers with webcams and microphones, why *wouldn't* they want to use them for something as important as a job interview?