That scenario was the same for us when DH and I had our first colonoscopties back in 2009 before ObamaCare. The line is as that person found out . . . the screening test is covered as preventative, but if they find and remove polyps (highly probably) the procedure is no longer preventative. In our case, I had 3 noncancerous polyps removed while DH had 2 (1 noncancerous and 1 precancerous).
It is quite the catch-22 in my opinion. My insurance wouldn't cover it based on it was initially coded by the doc doing the procedure. With some bitching for recoding, I got everything covered 100% for DH and myself.
This may be a case of needing to be an active and informed consumer, looking out for yourself. Admittedly, we were forewarned that should a polyp be found, that would trigger the procedure from being preventative screening to a surgical procedure. Fussing after the fact, however, saved us thousands!
p.s. In our case, I was 51 years old so it was the "over 50" recommendation for preventative services. My DH was only 48 but due to family history of colon cancer, the insurance company initially waived the 50 y/o requirement for coverage under the preventative clause in our policy.