Why, you stated 25+ million.. It's just an assumption.. 25 Million would mean 35 Million in others, I don't see why it would not pull that off.. And you said atleast 25 million correct? So if it sold 30 or 35 million that would not be totally off.. And this is just in the US alone? So you are not even counting Canada, South America or Mexico?
- It sold 45 million units in the US, it seems you're all using that number.
- Going by this Wikipedia article (which seems to use credible sources) it's above 8 million units in the UK.
- It was heavily outsold by the PS3 in mainland Europe.
I don't think they'll increase marketshare in mainland Europe (it seems they're even losing some) and the PS4 has a lead in the UK. In the US the PS4 and the X1 could be "tied" (an advantage of 5 or so million units, not more).
And we have to keep in mind that the Xbox 360 was easily hackable. I'm sure that helped them to sell some consoles in countries where the average income is lower. The PS3 was harder to hack (homebrews require your console to have 3.55 OFW or lower, right? Which is imposible for newer machines)