I am just taking a stab at this, but I think Boulder et al. targets a different (sub)market than the big boys, which affects their respective product goals. Similar to what has already been said, the big boys cater more to the casual enthusiast, etc. while the smaller outfits are more prestigious for and respected by people further in to the hobby.
high-end vs. ultra high-end amplifiers
It is quite frustrating to know that some amplifiers (Boulder, FM Acoustics, Accuphase) are sounding better than even very expensive ones from the big boys (Mark Levinson, Krell, Bryston, Spectral). I wonder why there is such a difference. Madrigal, Krell, Bryston, Spectral, they all belong to the high-end sector of audio industry and they are claiming they are making the best amplifiers. But I know that this is not true: I've heard amplifiers from Boulder and FM Acoustics and they sound just better than the Madrigals, Krells and so on. Is it because Boulder and FM Acoustics have more know how about amplifier design (I suppose not) or do they use more expensive parts and better circuit topologies? Do they have brighter technicians and designers? There must be an explanation for this phenomenon. It isn't magic! Maybe someone from the audio industry can reply to this thread.