An important part of the precision approach environment is the airport
surface itself: an adequate runway clear zone and adequate approach
lighting. Just because you can get a WAAS signal does not mean a
particular runway is going to be appropriate for a 200 ft minimum.

For whatever it's worth, the runway markings, taxiway spacing, and obstacle
clearance areas are what make for a 200-foot Decision Altitude (DA).
Approach lights (ALS) are for visibility credit. With everything else
satisfied but no ALS the DA will still be 200 feet, with a visibility of
3/4. Add ALS to that environment and it becomes 200 and 1/2.

For now, the lowest possible DA for WAAS approaches (LPV minima) is 250 feet.
Getting down to 200 feet (GLS minima) will require major system changes,
probably including a second civil GPS frequency, and will not happen before
2013 at the earliest.