With a mobile game, you're limited to touch interface. Most games that work great with touch, will still work well with a mouse and keyboard. The reverse is not necessarily true (think RTS on mobile... just doesn't work)
On PC you will hit technical limits a lot later on. You can have a far higher polycount or number of NPC's running around on screen before things start to get sluggish
Yes you could make something as technically sophisticated as angry birds without running into those limitations on mobile. But you can't afford the marketing budget required to be the next angry birds. At least with PC, you don't have to buy extra devices to test your game on
Also, you've got more options distribution wise. It's not like there is only one app store on PC and you have to pay 30% to be on it. With greenlight, your not going to get on steam until you're already popular, so why not just get a paypal or amazon "purchase" button on your website and pay 5% transaction fee in the meantime?
Edit: Also with multiplayer games, you can make some reasonable assumptions about how much bandwidth players have, how reliable their connections are. You can't make those same assumptions on mobile
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PS The link in your signature is wrong.
Thanks for the warning. Should be fixed now