It's about a thingie called 'Z Order'...what shows on top of what...and it's something shell themers have to deal with quite often...and a lot of fun can be had when running, say, Hoverdesk under LiteSTEP...the Z-Order can get quite 'interesting'...
That said, 2 of the most useful 'thingies' that WB is capable of providing is 'Ontop' and 'rollup' support....functional advantages for a GUI, not simply aesthetics...
