Why do popular post have so many down votes?

This always amazes me. I haven't been a redditor for that long and it always amazed me how most or all of the front page post only get between 51% and 69% up votes. For example:

This posts is front page with 1,300+ points but only 53% up votes.

This comment only has 52% up votes

Even posts that are completely non offensive, cute, heartwarming, etc, get down voted like crazy..... can anyone explain this?