Valuable perspective, but it is only one perspective (the IT manager). And I'm not sure it is really relevant since the recommendations at MacRumors.com are not for IT buyers but for personal use buyers. From the "Having to manage my own machine without support from a professional" perspective, a Mac has consistently been the best choice. Yes, they cost more, but I have fewer headaches (though by no means none) related to managing them in the handful of hours each week I have to use it when I'm not earning a living.
Furthermore, your experience is different from other IT managed scenarios in that you are managing for children, and the computers are shared resources. As I recall a couple of years ago there was a /. article about how IBM had moved to letting everyone select their own device and found that Mac's resulted in disproportionately fewer help desk tickets. The money spent on hardware resulted in savings from support. Your mileage may vary of course
I've personally helped dozens of people switch from PC's that they never really felt comfortable with, to Mac's which enabled them to get more from their machines. That kind of productivity gain and piece of mind can't be tabulated on a spreadsheet and so therefore has essentially zero value in an IT managed scenario, but for the day-to-day user of the machine it has great personal value. That is why Macs do so well with people buying their own machine, but not at large corporations.
Finally, the older MBAir that hasn't been updated will probably never be updated. The differences in portability between the Air and the MBPro are almost meaningless at this point. It exists in the line-up to hit a certain price point, and do so profitably. As long as it can fill that role, and still sell in meaningful volumes, Apple will keep it around. It's good business, regardless of what flamebait writers say.