I think that a lot of these subs have the opposite of what you are thinking. A lot of micro subs now will play as low as they dare, even down into the teens hz, but will reduce low frequency output as SPL increases. This way, they are only flat when playing at 75-80 dB. The dynamic DSP knows how much power the amp has and how much excursion the driver has and throttles back the bass accordingly at higher SPLs. DSP makes it so a tiny box can play to sub 20 hz or can play to 100+ dB, but physics dictates both can't happen at the same time.
For a studio monitor sub like he Neumann, the designers would much rather the sub go into protection or distortion rather than exhibiting a non-flat response.