It's funny, the Steam Machine has a weird identity problem.
We talk about it like it's a PC, and what a detriment it is to not be able to upgrade the GPU, like why else do you have a PC. But you can't upgrade console GPU's either. And it's still a plug-in-and-play box, no building required.
We also talk about it like it's a console, and what a detriment it is that a console costs over a thousand dollars and is digital-only. But the next generation consoles are almost certainly going to be as expensive if not more, with no disc drive either.
The SM is a glass half full and a glass half empty. It's the best of both consoles and PC's, or the worst of both worlds.