Are people seriously framing their arguments in a world where console exclusives don't exist, console games never go on sale, and everything on Steam is 90% off?
"Why buy consoles?"
Exclusive games and ease of use
Unless something changed and Uncharted 4 (new Zelda, Halo, GoW (both), etc.) is coming to PC, consoles will always have great games exclusive to them. SteamOS is designed to be friendly, but it's still a computer at the end of the day. At some point, someone will be told to open up Synaptic or a terminal to troubleshoot their Steam machine. That just doesn't exist on consoles.
"Steam sales are amazeballs and consoles don't have them"
This is a true statement.
So you're telling me that if I want to play GTA5 at launch, I can only pay $6, because it will be on sale? Oh wait. Launch prices are the same on both platforms. Oh, and GTA5 is not going to be available on SteamOS. SteamOS's library is growing, and getting some AAA love, and that's great. But it's still missing a lot of great stuff that will likely never make its way over. Of those 4500+ titles, how many are crappy indie games? Given time, I see their library growing, but initially library size is a valid counterargument.
Also, console games go on sale. The discounts aren't as deep, that's true. But if you're waiting for sales, you get sales on both. Consoles have the benefit of not locking a purchase to your account, so for the people that trade-in games, their equivalent price is the same or even better at times than Steam sales. Tons of console gamers buy at launch, play it hard for a couple weeks, and recoup 80% of their cost. This doesn't exist on Steam.
And there's the cost of the machines. At best, you have the $50 Steam Link. I actually like the idea of that device. But what about Steam machines that are intended to play the games locally? The machines that cost the same as consoles will play at an equivalent or worse quality than consoles. So now if you want to see what PC gaming is all about, you're paying at least a hundred more, but likely at a minimum $200 more for 1080p30.
And then, the issue behind the streaming devices. You're now occupying two devices in the house. For those in a family environment, that just won't fly a lot of the time. It will still have its times where it works, but one family member hogging two devices at once is selfish.
Steam machines are a good idea. I like the idea of packing all the power into a smaller form factor, and making it a no-compromise television solution.
But consoles won't go anywhere, and console-primary gamers won't flock to Steam machines.