I think that 2D building footprints is a feature of the MAP. (which must be enabled in Firmware as well, I guess)
For 3 years now my Nuvi 1300 has shown 2d building footprints when using pre-loaded Garmap Maps. (At some zoom levels in certain areas.)
The footprints are also visible in Mapsource on Garmap maps.
Maybe Some Nuvi's have the Feature disabled.