Why is RCN in Easton PA making customers get digital converter boxes and charging 8.95 a month more?

All of the cable companies are dropping analog channels in the near future.
They are doing this in an effort to offer more HD (High Definition) programming.
Newer sets with digital tuners will work without a converter box but older sets with analog tuners will go black.
The $8.95 fee is a rental fee for up to four converter boxes.