Windows and corrupt registry issues

So my computer crashed and can't start up anymore because of a missing .dll. This isn't the first time it's happened, and it's probably not going to be the last either. I'm not really angry, since the issue is easily fixable by repairing the registry with my Windows CD, but I am very curious about something. It seems like windows has a handful of core .dll's that must be intact to support the kernel. My question is, if they are so vital in supporting the system, and they don't take up much space, why aren't there simply 2 dozen copies of each one in the registry? Wouldn't that make Windows much more stable, since if one goes corrupt or missing another can be used to replace it? If there are any computer programmers out there, I'd appreciate it if you could enlighten me.