It's mostly a toy for hobbyists.
No, it's not. Just because not many have managed to make a living with it yet, doesn't mean it's the fault of the tool.
While HTML5's platform compatibility gives you the ability to export to any platform, it never really excels at any of the platforms it works on.
It's a jack of all trades, master of none.
Most games don't need more than c2 provides. Even CC, which is native, doesn't have that much more capability than c2. Also, don't underestimate the value of the ease of porting. I'd take that over using a framework that's a 'master' of one platform any day, since it doesn't give that much more capability anyway.
While you can make Android/iOS games from the same HTML5 project, both their performance and functionality are very limited. You have to work with really large limitations, both performance-wise and in terms of what you can implement in your games.
You can export a project to PC as an .exe file, but you have very little control of the file system, and you're never running "native" - it works through a bare-boned version of Chrome called Chromium. While it's compatible with any PC out there, Chrome/Chromium tends to give different results on different PCs. For example, after applying a coloring-effect, a cloud appears Green on my PC and Red on friend's.
You can read, write, execute, append, move, list, rename and delete files to disk via node webkit, as well as create folders. Most games won't need more file access than this, and if you do anyway, the SDK can be used to ake a plugin for it via the SDK. There are still issues with some webgl effects, true, but they can be reported and a lot of people are working to get them fixed. Also keep in mind that even tools used by AAA game studios have bugs in them. Writing a cross platform game framework is quite difficult when it's expected to run on tons of different hardware configurations and software drivers.
WiiU is something that is in the works of being implemented, but really, who has a WiiU anyway?
Something like 4 million people who are starved for games on the system. It might not be enough to develop exclusively for, but it certainly wouldn't hurt with how easy it is to port to other platforms.
Ouya - Look at android section.
I read that cocoonjs has plans to support ouya.
PS and XBOX have we no news or info about.
Microsoft has stated win 8 apps should be able to run on Xbox one, so it's likely that will work with c2.
All that said, it's still a hobbyist tool. I don't think i've heard of anyone earning more than a few hundred bucks a month with Construct 2 Games/Apps. And there's less than a handful of people doing that.
There are people making a living using it. Also keep in mind games take a long time to make, even with a tool like c2 that does a lot of the work for you.
Anyway, the point is that html5 is still pretty new, and is improving. There are a lot of people at a lot of different companies working hard to improve it. It may have some issues now, but they should be ironed out relatively soon.