That's only true for Microsoft. MS relies on the US/UK a hell of a lot more than Sony. The US/UK only represents ~30-40% of PS3/PS4 sales, whereas it's more like 60-70% for MS.
The X360 outshipped the PS3 by the smallest of margins, even though it had a year headstart and was cheaper (for a lot of the time, significantly cheaper). Sure having better multiplats helped, but that was a small factor IMO.
I think most would agree that the PS3 (earlier on, at the very least) was more reliable than the X360. So any advantage the X360 has could be chalked up to reliability and margin of error. But sure, I guess I will give it to you.
You could also argue that it was one of the contributing factors to the PS3's high price tag, which ultimately hindered PS3 sales, especially early on.
Power is, IMO, third on the list. Worldwide brand presence and price are both the two most important factors if you want to have huge success in the console market. Even though Sony fucked up with the PS3, was outsold significantly in two of the largest markets, launched a year late at a hefty price tag, it still managed to basically pull even. And even though the XB1 is managing to stay competitive with the PS4 in those same two large markets, the PS4 is outselling the XB1 by >2:1. Sony has worldwide brand presence, MS does not (at least not yet).
I would give 'power' more weight if the differences were significant enough for the average gamer to easily notice. Like I'm talking generational leap at a similar price tag.
It will probably have a ~35M lead.
I don't think it's that simple. I think the XB1S started outselling the PS4 (in the US and maybe UK only, I might add... by a small margin overall) for a combination of reasons:
-It was heavily marketed (borderline misleading IMO), cheaper, sleeker and a cheap 4K blu-ray player; so not only did it attract new buyers, but also appealed to existing owners.
-PS4 Pro was announced a few months early, with a release date close enough to hinder sales leading up to launch.
