My understanding of the analog bypass mode and the sub getting a full-range signal is that bypass mode by definition bypasses all sections of the unit that could apply any bass management. For those people who have analog bypass engaged with speakers that are full-range, bass management is not needed - thus they already have their speakers set to large. For most people, the mains are not truly capable of that (particularly if you are running bookshelf speakers that may start rolling off around 60Hz or above), and bypass will leave them a bit bass deprived. The solution apparently was to sum a copy of the left and right analog signals and pass it to the sub when the mains were set to small and analog bypass was enabled - which, in the absence of any A/D conversion to allow for digital bass management, was pretty much the only way to deliver anything to the sub. That's my understanding as to why the small speaker/full range sub signal in analog bypass is an intentional design decision. As you say, of course, this behavior is avoidable in other modes.