I had a virus that did that a while ago, I just went to my other computer, exported the HKEY_CLASSES_ROOT\.exe and imported it on the fubar'd one. Worked a treat.
Im sorry but if you cant see how its a stupid design then there is no point with this any more. If you think that you would ever not want to open a .EXE file in an application and would instead want to open it in something like wordpad then fine you can keep thinking that.
Actually, what if you wanted to try and reverse engineer an .exe? then you would want it to open in something else wouldn't you? Maybe not wordpad though. So no, its not really a stupid design.!