I suppose that, instead of creating an Ethernet-Zigbee gateway device and a bunch of Zigbee devices, one could also just make WiFi devices, if the chipsets and firmware support infrastructures are developed out enough yet so the costs compare favorably. But a quick survey suggests that WiFi still isn’t there yet. Lantronix makes the WiPort, an embeddable module which is sort of easy to use, and Mouser distributes it for $120/1, $100/10. DataHunter makes a G device called the Radion, which is $80/1 Nanoradio, and similar vendors make chipsets and modules which come way down in volume, but these are hard to get, hard to find dat for, and I believe don’t provide the TCP/IP stack etc. So, from my perspective, that of a glorified hobbyist, WiFi is still far too complex and expensive.