Do the commendation votes at the end of of a match matter?

What you see is what you get! It's just an opportunity for players in the match to commend each other on good gameplay. :)
_{@PlayOverwatch on Twitter (May 30, 2016)}

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Cards can reach "Epic" or "Legendary" status at 5 or 10 votes respectively. The only 'reward' is a unique voice line from the hero on the card. There's a full list of commendation voice lines on the Overwatch Wiki.

In other words, commendation votes are like clapping. They do not have any long-term tangible impact.

Right now, it's just for the lulz :D

They might add something points related in the future, who knows.