What stops them from saying 155m+ then? I still think that xbox is over tracked
Again, that is just not a "nice" number for a financial analyst. Once you get to certain thresholds, like 100 million, then you only report in big round numbers like 10, 20, 30 - unless you really need show progress or something (like, at the last milestone you said 130 million, and now it's three months later and you are only at 136, then you say 135+ so it still looks good).
Like I said, Xbox could be anywhere from 42 to 51 million. I bet VG Chartz is actually really close.