1 - Amazon rankings aren't useful to make these kind of extrapolations
2 - clearly it is very likely the majority of existing Halo fans who have a 360 will buy this game and account for the bulk of its sales
3 - it is also fairly likely the title will attract a percentage of new players to the Halo franchise, and will drive a modest, if likely short lived, HW boost.
So, will it be a system seller in the sense of significant percentage of additional HW units? Probably not, simply because the bulk of those likely to buy it should already have a 360 / Halo 3.
However, it likely will sell some systems, and produce a boost for short period of time to 360 HW.
So it depends what you mean by system seller, really, and everything is pretty easy to work out from available info and common sense without looking at Amazon.
Try to be reasonable... its easier than you think...
