I agree this behavior of full-screen mode is counterproductive on multi-monitor set-ups, and it's a serious issue if Apple is encouraging app developers to rely on this behavior instead of providing more useful window layouts. It's a violation of metaphor: "full screen mode" is actually "dedicated space mode," which isn't what multi-monitor users expect or want.
From personal experience, I suspect this feature is intended to make Spaces more accessible to novice users on laptops without external monitors, a common case. I never got the hang of Spaces originally, but once I started using full-screen mode while portable, my laptop got immensely more useful. For me, this was a gateway into the rest of Spaces, and now I maintain 3 desktop spaces and 1 full-screen app, and switch between them and Mission Control with trackpad gestures. Heck, I might even start using Dashboard, since it's sitting right there. (Ok, probably not.) It's a gradual introduction to an advanced feature.
Apple routinely cuts off its long tail as a streamlining measure, sometimes for UX reasons, sometimes for engineering reasons. They shouldn't always get away with it. At least in this case the intent seems reasonable, even if the side effect isn't.
From personal experience, I suspect this feature is intended to make Spaces more accessible to novice users on laptops without external monitors, a common case. I never got the hang of Spaces originally, but once I started using full-screen mode while portable, my laptop got immensely more useful. For me, this was a gateway into the rest of Spaces, and now I maintain 3 desktop spaces and 1 full-screen app, and switch between them and Mission Control with trackpad gestures. Heck, I might even start using Dashboard, since it's sitting right there. (Ok, probably not.) It's a gradual introduction to an advanced feature.
Apple routinely cuts off its long tail as a streamlining measure, sometimes for UX reasons, sometimes for engineering reasons. They shouldn't always get away with it. At least in this case the intent seems reasonable, even if the side effect isn't.