If that was the point you were trying to make why didn't you actually write it, instead of going on with a load of nonsense about users having to worry about which DE toolkit an application was built with?
It's not even a very good one point - given the vast difference between Linux and Windows' *minimum* memory usage there's plenty of room for an Ubuntu box to load the toolkit from another DE without even using up the minimum memory usage for a Windows 7 or 8 box. Not to mention that different Windows applications use multiple different GUI toolkits, so your average Windows box in use will need even more memory to work.
If you want a real world example: I'm running 64-bit Kubuntu 12.04 with bells and whistles like desktop effects turned on. The computer's been up for nearly 2 days, in which time I've run applications using both KDE/QT, GNOME/GTK and Mono .NET GUI toolkits. I have Firefox running currently and memory usage is only 1GB, that's half the *minimum* requirement for 64-bit WIndows 7 or 8.