It's true both in Windows and Linux that it's a non-routable address. It's false both in Windows and Linux that it's an invalid address. It's also false that 0.0.0.0 is "the same as 127.0.0.1" in general. That it's a valid but non-routable address makes it a good address for applications to assign a special purpose to. You'll find that in some cases 0.0.0.0 means localhost, but in other cases it has other meanings.

For example, you might be in for a nasty surprise if you assume that "nc -l 0.0.0.0 1234" is equivalent to "nc -l 127.0.0.1 1234".