Even ESC or ENTER seem more appropriate to me [for "bring up a menu or something", remark Christoph.Krn] than space.
You're thinking about what they're called. It doesn't matter what makes sense to use based on what it is named, I meant it makes sense because of the size and the location. A double width key in the bottom row is easy to locate and hit without having to hunt for it, and without fear of accidentally hitting it when you don't want nor of hitting buttons beside it when you do. It didn't need to be space bar, "B" could have been double width and it would have accomplished the same thing, [...]
Just a sidenote:
This is arguable, but most people probably won't be invoking game-pausing menus insanely often. In that sense, it isn't usually really important whether the menu key is extra big.
That is, as long as the user /
knows/ which key will invoke the menu. The space key is not necessarily the first key a user will think of when it comes to, say, exiting a software. What's worse, when the user is using the software for the first time, then maybe she doesn't even know what would be found in that menu, or that the menu even exists.
An important part of usability is to make sure that the user's imagination of how a system works does not mismatch the actual workings of the system in such a way that it will lead to results that are undesired by the user (see, for instance,
How Can Mental Models Be Applied in Software Design?). This can be achieved through a variety of measures, and one of them is familiarity. So, it makes sense if a game-pausing menu is bound to, say, the "Start" button, because that's typical on gaming consoles.
Wherever binding the menu to the "Start" button is not possible, it can make sense look at /
why/ the user may want to invoke such a menu. For example, it could be imagined that users may want to find this menu when they want to exit the software, hence it could make sense to bind the menu on keys that are associated with exiting a software. One of these keys could be Esc.
Moreover, it even makes sense to bind the menu to /
multiple/ keys and buttons, as long as this does not result in accidential invocations of the menu. In this sense, it's not a bad idea to bind such a menu on the Space key, the Esc key, the Enter key, or possibly even, say, Alt-F4, at the same time.
You might think that that multi-binding might not be all that much of an improvement, but familiarity is so important that a good rule of thumb in usability is that you do not change conventions. Think about the controversy surrounding Canonical's decision that the window control buttons in Ubuntu should be on the left side now, and you get an idea of the subtle effects at work here. Now imagine how frustrating it can be for people if you expect them to find out that to open a menu, they would have to press the B key, based on the reasoning that this is the biggest key (as suggested in the hypothetical scenario you provided). You would have to make sure that the information about which key to push is actually conveyed to the user at the right times in the right ways to prevent frustration or even panic, but most developers are not aware of these things. What's worse, situations such as failing at exiting a software can easily cause users to get into user-panic mode, where broad and creative thinking is difficult, which can cause people to miss obvious clues and instructions, push only the same few buttons again and again even though nothing is happening, and so on (
you don't have to be stupid to have such a thing happen to you Edit: Wrong link, this is the correct one:
you don't have to be stupid to have such a thing happen to you).