Thanks Don and thinking further...it appears that you may be hinting that we can't be totally certain about who exactly was attending Epicurus' Kepos, and what types of people attended the Epicurean communities. And yet, I don't think that it would be correct to compare Epicurean communities with early Christian communities. The teachings are very different and they will attract different people.
We see in Lucretius that there is an emphasis on the natural physics with the majority of DRN focusing on the causes of things, so as to dispell the incorrect beliefs about gods causing natural phenomenon. We need to ask ourselves what types of people are interested in this focus, and to see that this aspect of Epicurean philosophy was shining the light on Nature as moving with its own driving force, and this was an "early science" to examine the world and learn about the things that causes various phenomenon. The study of natural physics requires a certain intelligence level, and so then these would be the people more likely to have aquired the skill of reading. So I still stand by my hypothesis that most people who studied Epicurean philosophy in ancient Greece could read.