SUMMARY One can already set up rules to change a window's opacity... why not also add the option to enforce blur? Right now this can be done through shell hacks or the Force Blur script, but something that would apply globally would be great. Or even have some sort of toggle that says: Apply blur to every transparent window/context menu.
There are a few reasons why this option won't be added: (a) We don't want to introduce any new options, we already have too many. Extensible program is better than configurable; (b) Whether background has to be blurred is app's decision, there might be rounded corners, etc.