Thanks for your questions.

How is this done?

It is explained in the video from Chris that I posted in a comment above (from 13.00). There isn't a direct earning from upvoting or downvoting emails, but with fewer low-quality emails being validated, it should increase the CTP earnings pool for those participating in the validating of emails and making validated emails. 

Does the change in voting really assure this?

Yes! But it could also work out better in the other directions if you make a good email. The impact of the top 50 ListNerds holders will now be quite dramatic on whether you will get an email validated or not. Therefore 1 downvote worth between 5 and 10, for example, could stop your emails from being validated, whereas before it was worth just 1 and you didn't need to worry so much about getting a downvote.

I hope that helps! :)