You have to realize that Bose customers are not audiophiles. They tend to be non technical types that are not interested in knowing anything about what they are getting other than it seems to sound good to them. Consequently they are easily taken in by the Bose marketing. The marketing tells them that Bose is, "the most respected name in audio"! It isn't true, among audiophiles Bose is a joke.
When I see someone in a checkout line carrying a Bose product I really want to tell them but I don't. I think forums and responses to questions here can be a good place to inform people so maybe a few will avoid wasting their money.
I have to say however that another problem is the fact that most of the more respected name mass market loudspeakers out there are also not very good. It's only in recent years that harmonic distortion is considered in loudspeakers and most well known brands still don't consider it. As recently as the 2000 CES when I talked about this to manufacturer design engineers I got a deer in the headlights response out of them. Finally higher end brands are considering and measuring this today.
Another design consideration not considered in most mass market brands is power response. Conventional speaker are very non directional at low frequency and become directional at high frequency. This makes it impossible for them to illuminate the room uniformly. If they are equalized for a flat response on axis then the off axis is not flat and thus room reflections do not match the timbre of the direct sound field. This makes them sound fat, muddled, and even boomy. If they are equalized for a flat in room response at the listening position then the direct sound field is lacking bass and thus sounds thin. There is simply no way to fix the problem with EQ. Fixing it requires a departure from conventional speaker design toward either omni which radiates uniform frequency response in all directions...makes all frequencies non directional like the bass or some kind of broad band directivity controlled design that makes the bass directional like the high frequency. Dipole for example the off axis low frequency radiation is cancelled thus creating directional bass. The more uniform the power response the more similar the reflected sound will be to the direct sound and thus the more natural the speaker will sound.
So in short, most of the other speakers out there are pretty screwed up too. Consequently non critical ears have a harder time telling the difference between say Polk or other similar brands and Bose at least at first glance. Where they will be able to tell the difference is in long term listening secessions. Bose tends to utilize various forms of distortion to achieve an artificially larger impression of the sound. Enhanced mid bass, lots of higher order harmonics, lots of stored energy AKA time distortion... This tends to make their speakers very fatiguing to listen to long term. I've observed this in Bose owners, they tend to show off their system by cranking it for a few minutes and then saying, "doesn't that sound great"! Then they turn it off and go do something else. People with truly great systems on the other hand turn it on and it stays on..."just one more song...just one more song...". So in my opinion what Bose does is a bit of a crime in that they deprive people of the true enjoyment of music.
As the industry gradually catches up with the technology being developed by DIY'ers and the more research intensive manufacturers sound quality will eventually improve enough in the mass market products that Bose will either have to change with the times or they will finally fall behind despite their best marketing efforts. Right now the mass market just isn't good enough to make the overwhelming difference at least in first impression listening.
Another factor that might cause some to really like especially the Bose cubes is the fact they are omni directional at least up to a point. Their being so small moves the transition point up higher in frequency so they remain omni higher in frequency than larger more conventional designs. Some listeners may be appreciating this improvement significantly enough that it over rides other short comings of the Bose. For that one aspect of sound quality the cubes are better than most other mass market designs so maybe we shouldn't criticise their fans too much. If they are picking up on this then they may have a better ear than we think but if they recognize this they need to look for other solutions that retain the more uniform power response without all the problems of Bose.
Actually even the 901 while still non uniform like other speakers, it is designed to be mostly reflected sound. If EQ'ed to be flat at the listening position most of the contribution is from the reflected sound and very little from direct so it is still more uniform than most conventional speakers. It is of course very ambient but some may also like this even though it's not really realistic.
So your answer may be that Bose has some advantages over most other speakers in that both the 901 and the cubes may have a more uniform overall frequency response. It may not be flat but at least its more uniform in terms of the uniformity of the distribution of direct and reflected. I've often thought the 901 might not sound bad if built with better hardware. Tang Band and several others offer low cost small full range drivers that are dramatically better than those found in the 901 so if one were to build their own version of it using some of these better drivers it might be pretty good as far as highly ambient speakers are concerned.