That's a nice item, Tiermann. I think the display items are sometimes glued to the base of the case to stop them sliding- or "walking"! I bought a PM camper van once with traces of gluegun-type glue in the treads of the tyres- luckily it came away (with a pin and some effort) and left no trace.
I have seen a few display cases offered for sale on eBay, including a couple of Super4 ones which I was totally outbid on
I think the retailers have to send the displays back most of the time, though. Our (former) local toy shop said a PM rep came to set up and dismantle their PM window displays.
On the subject of PM promo displays, here's a nice one I saw last summer in Jarrold's department store in Norwich.
(mind you, it was in a little-used stair well).