Linksys's WUSBF54G appears to be the same reference design as Zyxel's AG-225H: I reviewed Zyxel's version, a combination USB 2.0 802.11a/b/g adapter with Wi-Fi detector, a few weeks ago. Zyxel's was extremely well made, and the description and captures from Linksys's product look essentially identical--except Linksys supports just b/g, not a/b/g.
A fair amount of commodity electronics--inexpensive, useful, mass-market devices--are created by firms that don't have a retail sales presence. They develop reference designs which are shopped around to retail brands like Linksys and Zyxel. The companies license the design, create their own wrapper, and sometimes their own software, and sell the product.