I have wondered the same. I wonder how it compares to other bluetooth speakers - Sony SRSX3, JBL Charge, UE Boom. I own a Bose Soundlink Color and several Sonos Play:1's. I am anxious to compare when my echo arrives on Feb. 20.
I have not tried the Sony, JBL, or UE. The Bose Soundlink is one of the best I've ever heard for a Bluetooth speaker. The audio from the Amazon Echo is not nearly as full ranged as the Bose. The Echo falls short on the low range. In the mid and high ranges, it sounds great.
If you bought an Echo and only wanted to use it as a Bluetooth speaker, you'd be better off with something else for the price. If the Echo was nothing else but a Bluetooth speaker, I'd say it's worthy of a $50 price tag. For everything else the Echo can do, a $200 price tag is fairly justified.