Why do translations use words like "servants" to mean "slaves"?

[Luke 12:45-48](http://www.biblegateway.com/passage/?search=Luke+12%3A45-48&version=NIV) uses the word "servants". What kind of servants get beaten up by their master? That looks a lot like slaves to me. We have an English word for that thing. It's called slaves. So why use servants? Servants are employees that got paid. Slaves are properties that got beaten up. Does the Bible translator bowdlerize the Bible to keep it politically correct?