Personally in our organization we like to save money but we also view buying a laptop as a very low cost expense. When an employee costs $100-$200k to employ (overhead, office space, janitorial, taxes, healthcare etc) a $1,000 system every 2 years or so is a tiny drop in the bucket.
At $150k / 40 hour weeks * 48 weeks = $79 per hour.
At that rate it only takes 10 hours of time savings before the computer (or $1,000 software) is "free". 10 hours sounds like a lot but if your employee has to wait 2 minutes a day for 2 years for a slow process you're looking at over $1,000 in wasted time. 2 minutes a day is a very very low bar for achievement.
Instead of trumpeting how much they saved on licensing fees, I would ask how much time they are saving--or are they? Is this just the IT department triumphantly cutting their budget or HR picking up the expense of extra employees to do the same work. That's the headline I would be interested in. If this saved them having 2 employees then they would save 400,000 pounds. If it meant they needed 3 more employees then they not only replaced the upgrade fees but actually increased their net budget.
I would suspect that WindowsRT like you say would probably be the easiest transition. I would argue that more than 2 minutes per day would be lost to Linux "hiccups" and confusion.