It's ll about minimising deployment costs
A lot of shops are still using Windows/7 or dare I mention it XP.
To maintain currency, that means around 80% of existing desktop platforms are going to have to be upgraded, although they have perfectly sound monitors, mice and keyboards, therefore the move to a "thin client" makes sense at a number of levels.
First off, they use considerably less power, even if you include the additional overhead of running more juice into substantial servers.
Secondly, you save a lot on licensing - only proportion of units are on at any one time and you only require that many tickets from Microsoft, which offsets the Citrix software overhead.
Most significantly, your support costs are reduced significantly- by operating a "standard" detop image, it is often far quicker and cheaper to delete the old (and possibly broken) session and replace it with a brand new one rather than debug it.
The final piece in the jigsaw is the thin client itself - all it does is establish a comms link with the server and run what is essentially RDP. the 'processing power' of the Pi hardly comes into question.
Finally, and perhaps most significant of all, unless you're moving to "touch screen" (3D, 4k monitors, instert technology innovation of your choice) it essentially insulates your desktop environment from back-office technology - these would remain "good" for many years to come, and with lower power, no moving parts it isn't unreasonable for these to have a service life in excess of ten years.
Of course that simply moves your "big ticket" items into the server room from the workplace, but it does permit the luxury of upgrading the entire estate in one afternoon!
A previous employer spent three years laboriously re-imaging 70,000 desktops from W2K to XP, and had to repeat the process over a similar time for W/7, once this kit is installed a changeover (with a generous six month lead-in) can be implemented overnight.
Finally the choice of RPI - it is literally a "building block" - proven design of inexpensive components, widely understood and bring all teh advantages of mass production. If you balk at the price tag, there's little to stop you buying the back-office technology and "rolling your own" on the desktop, although for most companies, the unit cost is sufficiently low to absorb the costs.
There's the added benefit of not leaving any confidential information in the "field" - the devices themselves would barely be worth stealing, and so you wouldn't have the constant headache of teh potential loss of confidential data.
A little overpriced - perhaps, but bring significant benefits to the organisation
(for the record I don't work for or have any financial interest in Citrix)
- sorry if that isn't isn't up to the usual witty discourse we're accustomed to on "teh register"