Valve doesn't publish figures on the number of Steam Links sold. But just look at the Steam Hardware Survey[1]. Valve recommends a quad-core PC to be used as the host[2]. But half of Windows users have two CPUs or fewer. The number jumps up to 64% when you look at OS X users. Meanwhile, the top 10 graphics cards are pretty well split betweel the latest NVIDIA cards and a bunch of Intel on-motherboard cards. I don't think the sort of enthusiast that buys a Steam Link is anywhere close to the bulk of Steam's audience; there are a lot of people who are playing games on laptops, not gaming laptops but just laptops.
I still find it very implausible that first mover advantage alone made Valve into a sustainable multibillion dollar company for so long with very little lock-in and very few anticonsumer practices. They have consistently outmaneuvered all their competitors for over a decade on multiple fronts. Their foray into hardware is just the most recent example. I think pointing to an outdated version of WebKit contained in the app is really grasping at straws for trying to find a way to make it look bad.
