In the end I gave up and created eight /27 masked subnets, where the last subnet is not used.
I think this is (almost) the solution meant by the author of the questions.
It's common for such questions to be written from time to time, and to be passed on and on through ages without adapting to actual technology. In this particular case, the author, I think, suggests that you cannot use a 'subnet-zero' i.e. subnet with all subnet bits set to zero resulting in 192.168.10.0/27. It was the case back in the days so you had to specifically permit usage of such addresses ('ip subnet-zero' in cisco ios). However, if you configure "no ip subnet-zero" you cannot use first subnet, thus giving only 7 usable /27 in a /24.
tl;dr: you're right, but the first (zero-th) subnet is not used due to an old currently irrelevant restriction
Back in the days of old, it was not encouraged to use all-zeros and all-ones subnets (RFC 950, p.6, "the values of all zeros and all ones in the subnet field should not be assigned to actual (physical) subnets"). So, borrowing 3 bits for subnetting, we end up with only 6 usable subnets. However, vendors started to support using all-ones and all-zeros subnets on interfaces. In cisco world, the all-ones subnet was supported without any configuration, and all-zeros support was activated by appropriate cli command, more info here: http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080093f18.shtml.
I've done a little experiment in GNS3 (cisco ios 12.4), so the results are:
1) you can use 8 subnets with 'ip subnet-zero' command (default)
2) you can use only 7 subnet with 'no ip subnet-zero' command.
3) classful or classless routing doesn't affect 1) or 2)