I agree that in certain use cases the Ethernet card is a bit superflous, but if you start that argument you may as well replace the whole Arduino, again depending on what you do and what your embedded coding skills are.
The TL WR703n hosts a 300Mhz Atheros processor (Arduino 16Mhz) with 32MB dram (Arduino MEGA 128kb). It has some GPIO and OpenWRT is an embedded Linux box. 8)