Is the basis for up vote/ down vote also commented or explained? The requirement could be important to OP because reward/punishment promotes learning.
It would not make things better to require a comment with every vote.
We encourage users to comment when they leave down votes, to help the OP know the reason for the vote. But if someone has already commented on a particular issue with a particular OP, or has a reasonable expectation that a comment might not improve the situation, it may be better not to post a comment at all. This has to be decided on a case by case basis.
For upvotes, users are discouraged from leaving relatively meaningless comments such as simply "good answer" or "thanks" along with an upvote. The upvote itself already indicates that the voter thought the answer was useful.