Unfortunately stuff like this isn't uncommon with games, and many other programs for that matter. I wish it wasn't as common though cause it is definitely an inconvenience
But it's correctable. Whoever is in charge of maintenance for the WGT installer simply needs to add steps 3 and 4 from ScottHope's link to the uninstall program.
I come from an IT background and I used to write programs to install/uninstall software. Adding those 2 steps really isn't that difficult. And doing folder and Registry cleanup automatically during uninstall is pretty basic stuff.