It doesn't matter how much of that 10% is just Skyrim sales, my point is of all the customers and profit they got from Skyrim, it was only 10% from the PC. In the end, it would be smarter to not even make it for the pc at all, save resources, time and wages on console and they could make up that 10% in just console sales.
If you cannot do maths, I'll count the numbers for you. We'll just use the data at the time of my quote(18th dec), as selling price is more accurate(at Christmas most retailers as well as Steam have cut the price down, so including the sales number during Christmas will be harder to get an accurate result).
At that time VGChartz showed 3.4m copies of xbox version sold, and 1.2m(not including digital version) of PC version sold.
Based on the reply I made above, as well as some assumptions, we'll calculate the revenue from PC vs xbox.
Two assumptions
1. Xbox version of the game is completely free of royalties, aka Microsoft gets zero money from the sales of Skyrim. This assumption is 100% impossible. Microsoft and Sony don't earn money by selling consoles(most of the times they sell the consoles at cost price), they earn money by getting royalties from softwares sold.
But since we cannot get an accurate number of royalty fee, we'll just make a favorable-to-xbox assumption.
2. Only half of the total PC sales of Skyrim are digital. The actual percentage of digital sales should be much higher, considering average PC games like The Witcher 2 has around 45% while this is a Steamworks game. But then, let's just make all the assumptions favorable to xbox and see what happens.
Now we can start ESTIMATING the revenue from xbox and PC. At that time most retailers as well as Steam are selling the game at full price(59.9, I know in some part of the world the price is higher while others it may be lower, but for simplicity's sake just assume this is the price for the whole world).
ESTIMATED revenue for Xbox: 3400000 copies x 59.9 x 30%(amount the publisher/developer get back when the game is sold at retail, not including console royalties)
=$61098000
ESTIMATED revenue for PC: 1200000 retail copies x 59.9 x 30% + 1200000 digital copies x 59.9 x 70%(amount the publisher/developer get back when the game is sold digitally)
=$71880000
From this estimation we can clearly see the revenue for PC is higher than Xbox. And this is not counting console royalties and assume the PC version only has 50% digital sales.
For Skyrim, it is no doubt that PC version constitutes a much higher percentage in revenue than people have guessed, probably the largest among the three platforms.
Saying the PC version only constitutes 10% of the total sales is a fallacy the developers often use so they can commit less to the PC.