Debian has a strict attitude to non-free firmware: since Debian 6.0 non-free firmware are no longer provided by a standard Debian installation.
The Wheezy/Testing installer however seems to go a step further and chokes if your computer needs non-free firmware. The solution is to rip out the wireless card that requires the non-free firmware.
OK, it's a bug* not a feature, and there is a workaround here.
* These seem to be the same bug: #681656, #683690, #684581.