I know what percentage represents, but what you fail to understand is that 45 % is still close to 55 % regardless of the quantity it repsents, that's what percent are used for, not to represent an actual number quantity.
1 % can represent a small or humongous quantity, but it's undeniable that it also represents 1/100.
Hence 45 % can represent as you have said 45 or 45 * 10 ^6, but the truth is still that 45 % is close to 55 % regardless of the actual difference between them, it's the percentage difference that matters.
If during all this generation X1 maintains close to 45 % marketshare, nobody can claim that PS4 dominated US, it will always remain a close battle.
I had made a point of not responding in this thread any more... but I can't help but use my Maths major to good use here.
I'm going to assume 55%:45% is a correct ratio of the marketshare like you have. Regardless of how many total console sales there are, this can be used to determine the 13% (and previously 10%) difference you quoted. (55-45) / 55 * 100 is a little over 18%.
As you rightly say, 45% can represent 45 * 10^6. But even using the respective figures of (55*10^6 - 45*10^6) / 55*10^6 * 100 is over 18%. And 18% isn't close. Not even in the ball park.