I think you are not correct on this point. You can't imagine the number of high end multiroom systems where Sonos is used for audio. It's an smart choice, as it's really flexible (you can connect directly a pair of Beolab to a Sonos Zone player and get a wonderful audio quality, Sonos DAC are not bad), and it's based on ethernet, so it allows huge installation where cheap competitors sells the dream of having only a wireless audio network (wireless Sonos is not a wonderful performer too, as is Beolink Wireless).
As the Sonos Protocol is based on a simple ethernet language, there are even companies who have developped gateways between home automation and Sonos (it should remember you something...)
BUT Beosound 5 Encore has some other refinements, like the ability to play HD tracks (it has to be proven, but if it's not the case it would be a huge mistake), or MOTS, which is a really clever solution for huge music libraries. What Sonos has and Beosound 5 Encore won't have (never, I think) is Deezer, Last.fm and Spotify. Later, I hope that the Beosound 5 (Encore) will get the same kind of iPad interface as Sonos. Why? Just because it's good to benefit of the two kinds of interfaces : linear interface for the Beosound 5 (allowing to browse the library like a stream of music), and "object oriented" interface, with a search field for the ipad app, allowing to create a specific party playlist, for instance.
To make a long story short : Beosound 5 interface is ideal when you don't know what you want to listen to, Sonos iPad interface (or Kaeidescape, if you're tempted to spend high) is perfect when you know what you want to listen to. Having both would just be perfect. I hope B&O has understood that. I don't want a Beosound 5 interface "copy" on their iPad app.
Of course, there will always be a kind of customers that will never take a look at Sonos, just because "it's too cheap to be good". But the comparison really makes sense, it's clearly not a Ferrari vs Fiat comparison. If you think of cars, see it as a Tesla Roadster (the new competitor from the silicon valley with no image but a great product) vs Porsche GT3 (the good old classic which has a high image value but is challenged in innovations...). Both can go from 0 to 100km/h in 3,7s 😐