Zwingle, simple... they made a 10/100 model so it could be used on 100Mbit only networks. Many companies will buy routers and switches that aren't 10Mbit compatible, as they are cheaper to manufacter if you know that you won't need the 10Mbit connectivity.
So, yes, they are slow, but they do have a use and purpose. They are very easy to use and require no installtion other than pluggin it in.