Right, and that makes sense. Larger dies are primarily a cost issue; they reduce yield, which increases cost per functional die. More development effort spent on MTBF is a resource issue; work spent improving MTBF is work not spent improving operating frequency, but with enough resources (money) it doesn't have to be a problem.
I could be wrong on this, but I believe IBM's AIX line is not cheap, if you see where I'm going with this.
You're definitely going in the right direction; Power5/6/7 hardware is very pricey. I'm amazed that in this day and age, AIX still has a place in many companies, and slightly perturbed that I have to maintain it. I'd much rather have the applications running under RHEL.
I could be wrong on this, but I believe IBM's AIX line is not cheap, if you see where I'm going with this.