Please cite those other sections -- I didn't see anything other than 15.247 covering communication devices, and the section heading explicitly states that it applies to the 902-923 band. Other parts of the regulations do cover the band, but NOT for communication devices (CAT scans, for example).
I interpret it as: heading - (communication) devices in 902-923, (a) then restricts those devices to frequency hopping (or digital). It does not leave an opening (in my view) for non-frequency hopping (/digital) operations.
Amateurs have access on a secondary basis and must accept any interference from ISM devices, and must not cause interference. They appear to be the only ones not required to use spread spectrum.
