Lol....

No, literally... Look into it.

From memory, I think sales on PC of big AAA games are usually equivalent to one of the consoles. This obviously varies quite significantly depending on the game franchise but on average, around a third of revenue of a PS4/Xone/PC title will be on PC.

Well, your logic is flawed and you're also just plain wrong in places.

Firstly, MMO's and MOBA are big business that you just conveniently ignore because it doesn't fit your view. There are literally millions of people that play these titles and they're constantly evolving. How any game that has millions of people playing and paying large amounts of money to play can be considered niche is beyond me. 

Using your logic you could just say "outside of FPS, sports games, beat-em ups and platformers nothing sells better than PC". It's flawed logic and plain wrong. 

@ bolded

Most Valve games sold better on PC (see below), as did Diablo 3, Witcher games, Metro, some Battlefield titles etc. Often, the PC version sells similar numbers to one of the console versions.

Yes the push for GPGPU computing did come in at the right time for them and they have made a lot of headway into the HPC space which has really helped them take the edge off the loss of the once high volume low end GPU market. It is a shame their mobile endevors didn't work quite as well so far but there is a lot more competition there and they were late to that market rather than basically creating it for GPGPU for HPC tasks. And of course binning reject super computer GPUs allowed them to discover that gamers are actually willing to buy a $1000 GPU for some reason lol.

Gaming PCs have always been niche and they always will be. As desktop PCs have gone the way of the dinosaur and laptops and tablets have taken over the PC market, there is even less incentive to get gaming PCs as well. Also, the majority of PCs that people game on (not just gaming PCs) are weaker than the Xbox One and most likely cost around the same when the person bought it. Why? Because the majority of PC gamers (not just PC gamers with gaming PCs) are content to play MMOs, Facebook games, or PC games on medium settings.

And 90% of Steam users don't have gaming PCs. 

interesting,  which orafice did that figure come from? 

I agree with your entire post and feel this is the biggest factor. I refuse to pay more than $20 for any digital game. I am not sure what the profit margins are on digital games, but a lot of PC gamers dont want to pay premium prices for digital only content.

Doubt it, the issue with steam is that is nearly impossible to know what the sales are cause they never release sales numbers but that doesn't really mean you need high end gaming pc to run all the pc games... Steam is filled with indie games that can run on the basic non-gaming computers and thanks to steam sales which happen every week and weekend and the big steam sales like the ones during beginning of summer and Christmas, more and more users are going into PC gaming, not as an the only gaming solution but a place to buy cheap games... And virtually all third party games are coming to PC so there is that too. If anything, the PC gaming scene is growing imo, specially since the entry point cost of a gaming pc is going lower and lower. I mean heck

http://www.joystiq.com/2014/01/15/steam-has-75-million-active-users-valve-announces-at-dev-days/

And on top of that, there are MMO and rts which are more favored towards PCs than consoles and the list goes on

Oh boy, pretty much everything you wrote is wrong but I'd like to highlight this one:

"3. In PC gaming people are delighted with the sale of an AAA game at $10. And why they shouldn’t? It’s a great offer. But from a developers perspective this is not a good sign. They want as many games sold at $60 not in $10."

Do you think console gamers aren't delighted by sales too? See the amount of praise PS+ receives for its "free" games or the huge used game market. I've seen enough treads of "oh, it is just a 6-8 hour game, I'll wait 3 months and pick it up for $20".