So let's say that Microsoft promised a market of X users.
Okay, great. Let's assume that for right now, X is 41 million.
Let's assume that of that market, (just for numbers) 1 million is using Surface tablets. So that's a market of 41 million WinRT API/Modern UI/Store devices. Got it. Limit yourself to the ARM devices only: You cut out 40 million possible users. Users like me, who'd actually purchase the game if they could even without a touch screen computer. (I wanted to play this on my laptop....)
Awesome. So you're stuck with 2.4% of the market of clients that could run your product, and you make 52 euros.
What if the same rate of people bought your product if you made it available to 100% of the market?
52 / x = 2.4 / 100 .... x ~= 2080
So by the act of clicking a SIMPLE CHECK MARK they could have potentially tapped this market. --- http://blogs.msdn.com/cfs-filesystemfile.ashx/__key/communityserver-blogs-components-weblogfiles/00-00-00-30-15-metablogapi/2112.image111_5F00_551F8980.png --- (yes, it's really that easy)
On windows 8, when you're coding for arm on an x86/x64 machine. your IDE and compiler and simulator are all executing x86/x64 code. You cross compile for testing on ARM device or for distribution. You get x86/x64/arm all at once. There are no code changes to make / porting to do. Limiting it to ARM devices only is a CHOICE of the developer.
Microsoft's design is that I should be able to install the same app on my tablet or my laptop or my desktop if I so choose. The developer blames Microsoft for not having an option that says "you can only download/use the metro app on tablet formfactor devices" and/or a way to enforce this restriction . The developer has a contract that says they can make this game for only tablet formfactor devices(for some awful reason). So to bypass this, they compiled it for ARM only to comply with their supposed restrictions.
They could have increased potential revenue by an insane amount. Instead they locked out 97.6% of the market.
Of course, some apps may be too heavy to execute on ARM so they will not be compiled on that platform, so won't be visible. However, There's no real justifiable reason to not make the application you're targeting for ARM available on x86/x64 as well, except for arbitrary legal ones like this.
What happens if someone makes a low powered touch windows RT pc? the app can now be downloaded onto that and it's not a tablet formfactor device.... and this violates the developer's contract.... But wait! this means the app isn't available on the Surface Pro! ... which is a tablet formfactor device running the windows store! Oh my, developer, you're going to confuse and fragment the market even worse than the simple split between Windows RT and Windows 8 being merely Desktop App and beefy CPU issues.