Haven't you calculated wrong?
I mean, let's say for 360 in America..
If you divide that 10.73 tie ratio with 211 weeks, you get 0.051/(console*week) right?
Maybe you missed it in my post, but I'm using 2*tie ratio/weeks i.e. there's a factor 2 in all the numbers.
Of course it doesn't make any difference when comparing, but if you're curious the reasoning is that since we're considering a constant average rate of sale for the consoles, then the average age of each console is weeks/2.