You must also consider people who are not native speakers. I'm sometimes appalled by the complexity of the letters I get in Germany, especially when they are related to immigration.
Essentially, yes.
Using words most people are familiar with will afford a lot of people nearly instantaneous cognition [0] of the information you are trying to convey with your writing.
This applies to both ends of the reading spectrum: highly educated people who do a lot of reading than most; and poorly educated people who probably had to drop out of school to make ends meet.