Admittedly they are small systems. 50 or so concurrent sessions - however, as they control 80% of the business flow in the company they are mission critical.

I agree, if I had to ensure 24x7 availability 1000 concurrent users I'd plump for something more robust, like Linux or Unix. Particularly with the state the Admins keep our network in!

Just don't assume that every Windows shop is a flaky, fly by the seat of your pants outfit!