From the AOPA website:

AOPA meets with FAA to work toward resolution of sport pilot medical
Catch-22

AOPA staff attending AirVenture in Oshkosh today met with FAA
officials responsible for the sport pilot rule to work toward a
resolution of the medical "Catch-22." Both in questions to AOPA's
Pilot Information Center
(http://www.aopa.org/whatsnew/newsite...0728sport.html) and at
various forums at EAA's AirVenture, pilots have expressed
disappointment that if they've been denied a medical in the past, they
can't use a driver's license in lieu of a medical to exercise sport
pilot privileges. However, a pilot with a similar medical condition
who has never applied for a medical, can.

"AOPA, along with EAA and other groups, is continuing the dialogue
with FAA to find a way to get back to the original intent of sport
pilot," said Andy Cebula, AOPA senior vice president of Government and
Technical Affairs. "If you're healthy enough to hold a driver's
license and you have no current medical condition that would make you
unsafe to fly a light-sport aircraft, you should be able to exercise
sport pilot privileges."