Is it overhead to the OS? The default window behavior would have to be changed to have a resizable border around the windows but then it bubbles throughout the rest of the system. It's hardly resource intesive. Far less than Expose and a transparent Apple menu, to be certain. How quickly we forget about OS9's (and prior) wasteful eye candy such as the flashing menu selections on far less powerful hardware -- and you're worried about whole window resize handles?
This was my point. My point was that all of the little things add up. I'm not saying that it's going to cripple the system. My point was also that it doesn't fit within Apple's software philosophy. I already mentioned that exposé (and dashboard) take up way more resources than adding the ability to resize a window from the borders. But, as I said originally and correctly, being able to resize from the borders requires more resources than the single corner alone. I didn't say it was a lot, I just said that it was more.
If you're going to go that far, why not add the ability to move windows from any spot (that doesn't already interact) by holding a modifier key such as command and clicking? Why not make it so that option clicking on the title bar sets windowshade mode? I do miss windowshade mode actually. How about command+option clicking and dragging within the window resizes a window to fit a selection? Maybe command clicking on an interactive UI element highlights all other UI elements that can interact. All of these things are relatively simple to do, and each wouldn't increase resources more than adding the ability to resize from window borders. Make sure all of those events have an associated animation too. Would you like them to add all of those UI interactions? I doubt it. Implement enough of those and you'll be staring at a beach ball each time you press a key. At the very least, there will be even more books trying to teach people how to use Mac OS. Is this a ludicrous example? Yes, but it illustrates my point.
And, that menu flashing behavior is still present in OS X. I believe they left that in OS 9 because previous versions of the OS could hang if the menu was left open. I assume the flashing was a sign that the menu hadn't frozen, though they could have just closed the menu. That's probably what they though of to make it interesting in those days and so it stuck. It's a character element, but yeah, it's a waste of resources. It takes relatively nothing, but it's still a waste.
Please don't assume what my programming experience is. You don't need to explain to me how to implement such features, I'm well aware of the process, thanks. And while we're talking about it, I've actually never made a "hello world" program in anything. I understand the purpose of writing such programs, but they're boring. In any class where I was required to do something like that, I always made sure to add something else to it.
And might I add a reason why it's inferior -- one can't grow an application window in the negative X and/or Y axis in a single step. In other words, I'd have to MOVE the window up and to the left, and then in a separate step move down to the lower right corner of the window and resize it. As opposed to grabbing the upper right corner and expanding it in a single step.
This, I will concede to. It's a good reason.