I believe that TXT and RTF are not for Joe Average anyway.
Any user who is aware of those two formats and the difference between them and how actually to find them on their own PC and transfer them to Sony reader, will be above Joe Average.
For Joe Average there is LRF format with Connect store. People who don't know what is "format", what is a difference between DOC/RTF/TXT, they will not be interested in the formats and problems associated with them anyway. It is not just Sony's problem. Cybook supports HTML...do you believe Joe Average will be able to master reading HTML formated books easily? I don't thinkl so. Joe Average will use Mobipocket.
How easy-to-use is Connect store it is another matter. I don't know. I don't use it.
The only drawback of any 6" screen reader is when they say they support PDF without any warning about "a must" to format pdf for 6" screen. Then again....maybe it just shows that I am Joe Average that I didn't know all the details about PDf being A4.....