When the Blu-Ray format first launched some companies seemed to (like me) prefer the US slimline cases so ignored the general edict that UK cases should be fat. More recently that practice (aside from ITV titles) seems to have gone away, although all Eureka's titles are issued as slimlines.
A real shame as I could stack even more if they were slimline cases instead of the waste of space the fat cases are.
In all honesty, I probably prefer the slim sized packaging also for the same reason, space saving.
My Tesco order arrived today in a "fat" case. I will probably watch it in the next day or so.