No you're right, it's mostly stereotypes that don't have any real world importance. From my intermediate POV, it comes down to GNOME being a resource hog which the 1337 H4X0Rz don't like. But with most modern systems having more than enough resources to spare, you're not likely to notice unless you're the sort to always have one eye on the system monitor pegged to your desktop. It's an argument for the sake of an argument. I use KDE btw.