Cat 5 cabling is more expensive than adding an adapter especially if the cable run is lengthy and then you have the issue of cabling laying on the floor unless you run it in the walls which is a lot of trouble versus a wireless adapter...
Well, I don’t know anyone whom would wire his house and leave Cat5 just lying on the floor—that’s retarded. If the distance is far, though, then these cheap Chinese wifi adapters may not be up to the task anyway. Also, what kind of range does the WAP have? Lots of questions here.