(1) It depends on the bass management of the AV receiver. There are others besides Outlaw (H/K for one) that let you operate in stereo with the subwoofer and the mains set to Large or Small (the double bass thing) with a selectable crossover setting.
As to setting mains to Large with the subwoofer and DD 5.1, there are users who simply want tons and tons of bass, so-called "bass-heads." I know plenty of them.
I'd agree that with other receivers that don't permit the above, then it would indeed leave the subwoofer silent.
(2) It could, but for bass-heads, it isn't a "problem."
(3) I've tried to explain this previously but other articles may omit it because it's technically complicated and the number of AV receivers and preamp/processors that enable this is in the minority. (And I might have omitted mention of it in some of my pieces because it's tricky to understand. . .)
Incidentally, lots of naive listeners equate bloated, fat bass with "warmth" in a loudspeaker's tonal balance. And it sells in retail outlets' speaker demos.
Regards,
