AVR-GCC != Arduino
Yes, but "no avr-gcc == no Arduino"
There's a lot to "avr-gcc", including the gcc core (not cpu dependent at all), the assorted "binutils" (also not cpu dependent), the standard and specific C libraries (avr-libc), plus the mere packaging (giving a windows gcc binary to a windows users is pretty useless without a unix-like shell environment, so "WINAVR" ends up including a bunch of standard unix utilities (rebuilt for windows) as well.