I did some scanning of the 14 CFR Preambles, which make it clear that
you're right on this. An excerpt:

-----------snip----------------

The FAA does not agree that some or all commercial sightseeing flights
in airplanes or rotorcraft should be excluded from application of the
rule. Commercial sightseeing operations usually involve members of the
general public who have paid for a ride in an airplane or rotorcraft.
For purposes of the antidrug rule, the FAA has determined that the
safety implications of such operations are comparable to that of other
operations that routinely involve carriage of passengers. These
passengers should be given the protection inherent in other
passenger-carrying operations for compensation or hire that have an
approved antidrug program, without regard to size or scope of the
operations or the number of flights per year a particular operator
might conduct.

-----------snip----------------