The move can be seen as one of Microsoft’s defensive mechanisms against the increasingly popular PS3 Slim, which doesn’t include 802.11n support. Who knows, maybe a retaliation from Sony is in order..?
There are a number of other reasons as to why Microsoft would release such an adaptor, rather than simply to ‘one-up’ Sony. Our American friends have the Zune HD, which features 802.11n and the new adaptor would therefore encourage friendly streaming between the Microsoft devices. The other major benefit will of course be Xbox Live, as recent routers are increasingly equipped with 802.11n capabilities.
According to Microsoft, the Xbox 360's 802.11n Wi-Fi adaptor will allow gamers to "seamlessly connect with their home network with the highest wireless 'N' technology."
More details on this new Wi-Fi adaptor will be posted when available.