I pretty much just consider it a continuation of Ellis' run. I mean, this mini is called Xenogenesis, and his last Astonishing story was called Exogenesis. But at 4 bucks...well, his run wasn't really that good.
More than anything, I think this is MArvel's response to people complaining about Astonishing X-Men always being out of the loop from the other X-stuff. Personally, I appreciated that fact. I don't read or care about any of the other X-stuff, so Astonishing was the easy choice for me to read. But of course, I guess most fans would rather every comic book be involved in a multitude of crossovers for it to be considered legitimate.