As a user, which I am, one difference between the products mentioned and Soda Stream's product is that it only takes me 30 seconds to prepare a soda of my choice. Bread maker's and Ice Cream maker's are a bit more involved and require time.
I understand how from an outsider's perspective, this looks like a fad like the aforementioned or even a George Foreman grill. However, from my point of view as a Sodastream user, it's wonderful and no fad, but a game changer. My Sodastream sits on my counter and gets used daily.
talked with my brother last night about the SS his family got for Christmas.....he was a big D Coke fan 7-8 a day....but now he is drinking 2 liters a day of diet cola from SS and going thru a syrup bottle a week....and that does not inclede the other members of his family who also use it daily