Before I start I wish to clarify that I don't intend to hijack this thread or to start any sort of argument.
FS normally are 3 way designs with Woofer+Midrange and tweeter hence they load amp with 4 Ohms in case the speakers are in 8 Ohms, So the More power is required to push the speakers to get Loud.
Well its not always that a tower will be a three way just like its not always that a BS will be two way ! There are tonnes of such examples.Also there are umpteen towers with 2.5way configuration,so making generic assumption is not right.
Even if the tower is a 3way then impedance of the woofer is the only thing directly loaded to the Amp as the midrange and tweeter both are connected via respective caps and its impedance (that of the Capacitor) is so high that its not reflected ! refer to the schematic below.
The Loudness of the speakers depends on the sensitivity of the drivers individually and total inbox (that is the sensitivity of the overall speaker) and nothing to do with the FS or BS or two or three way etc. For Example a 85dB BS will need 3 times more power to output the same decibel level as a FS with 88dB sensitivity and vice-versa.
But where as the 2 way or Book shelf speakers its Two way design and they would be run Loud with Nominal volume.
Eg, You try connect the FS and BS in same amp A+B and try listening the sound from BS would be good until you crank the volume and FS might not impress with at Normal volume level compared to BS.
With the above example I guess its already proved that what you say is not true.
If you need to experience then suggest you too visit the same place as the OP !!
As said in the beginning this is to just state facts and nothing more,so hope its kept that way.
Also if you wish discuss more then its better to open a new thread as I don't want to or intended to disturb this thread any further.