There are models that are pretty "low tech" that could be used for streaming primarily, but there are many others that are just straight up mini PCs. I see where you're coming from, but your point is sort of invalidated by the specs that just came out.
I don't think you're wrong, but I think the Steam machine has shot itself in the foot by not having some sort of tiered system. A big problem with the intimidating complexity of PC's is knowing what each part is and what the naming conventions mean. They're still looking at a list of specs and don't know the first place they should look. It's definitely easier than building a PC yourself, and I don't doubt that some people will finally jump into PC gaming with a Steam box, but you still have to get on the internet and look up just what the hell a GTX 770 is or the difference between an i5 and an i7.