I agree with everything you say. All I can say is I listened to these and the P362 level matched without subs and I preferred the bass of the Behringer. I can't say it went lower, but I would have noticed if it was substantially absent in comparison to the P362 (which is rated at -3db at 38Hz).
Behringer does state:
Ultra-linear frequency response from 55 Hz to 21 kHz, but I would be skeptical about what "ultralinear" means as presented by the manufacturer!
As an aside:
Interestingly, the Active Behringer 2031A is rated at 50 Hz to 21 kHz. I would assign certain attributes to an active speaker with active crossovers, but I would not expect extension to be one of them!
Any ideas on why going Active would give better extension?
With an active speaker, there can be a bass boost in the amplifier to make up for the drop off in frequency response of the woofer. However, in doing that, they would be increasing the likelihood of bottoming out the woofer, unless they also had built-in a limiter for the amplifier. That would mean, of course, that that frequency response would obtain below maximum output, but not at maximum output, as the boost in the bass would have to be limited at that point, or they would be limiting the maximum volume of the speaker.
As for the bass response compared with the Infinity P362, how much one will notice regarding any difference will depend upon many factors, not least of which is the source material. If one is listening to something without bass that goes lower than what the lesser speaker will do, the better speaker will not be playing any deeper bass due to it not being in the source material.
One way that some manufacturers have given their speakers the illusion of deep bass is by over-exaggerating the upper bass. So one gets a bassy sound, but without actual depth. I have no idea whether that applies to these speakers or not, or what music you listened to, or what the acoustic properties were in the room where you played them both (if they were not both in the same room, you can forget about seriously comparing the bass by sound), or how they were set up, or anything else that may be relevant.
And, of course, you are right to be skeptical about the meaning of "Ultra-linear" in this context. It is basically a meaningless phrase, like saying it is "good", or saying of an amplifier that it is "high current" (which is really funny when listed on an amplifier that isn't supposed to be used with speakers less than 8 ohms, presumably due to a lack of being able to deal with the extra current required for lower impedances).
