It's quite interesting to see some of the weird arguments people bring forward for declaring this a complete non-issue by claiming there's no reason for wired ethernet anymore.
Thing is: WiFi does have disadvantages compared to wired ethernet. For video games, the most important disadvantage is iFi's bigger latency, which is a concern especially for online multiplayer games where fast reactions are important, like Egoshooters. The effect may be moderate and is also influenced by the general speed of one's internet connection, but most people who often play multiplayer shooters online will want the best prerequisites, and that includes wired ethernet.
And of course there are people who don't have or simply don't want WiFi because of security or electric smog concerns.
In the end, this indeed is a non-issue - but not because nobody needs wired ethernet anymore, but because people who need or want it will simply be able to buy a wired ethernet USB adapter like the one that already existed for the Wii.