If I understand you correctly James you are pointing out that making a speaker with that FR specification is not a trivial exercise? If so that is my point. Throwing a generic commercial (albeit quite a decent one?) drive unit in a box is very unlikely to result in a response within 10dB up and down 100Hz to 10kHz. Also, starting with a free air resonance of 71Hz the system Fo will likely be well above 100Hz. Now you CAN run a speaker system below its system resonance but input power doubles per octave below Fo (IIRC, I know it gets big quickly) and distortion rises at an alarming rate.I just checked and found that the legendary LS3/5a small monitors are only specified to +/- 3dB between 80Hz and 20kHz. These are serious BBC designed monitors and a brand new pair would set you back just under £3k these days. Of course you can achieve better value for money these days with something like the Neumann KH120 but they are still above £1k per pair. The Neumann's claim a variation of only +/- 1dB between 100Hz and 10kHz.
And remember, that £3k does not include a very good stereo power amplifier.
Dave