Hardwired connection provides reliable, predictable throughput (up to the limits of the ISP connection and conflicting demands on the provisioned capacity). Some consumers are finally using Fiber Optic ISP services (e.g. FiOS). These can provide significant downstream throughput. (My connection achieves over 900Mbps downstream, even using sensitive single-tcp-stream testing.) Existing Roku equipment cannot make use of that capacity. The current Roku products are only equipped with Legacy 10/100 Ethernet ports. (And who knows, perhaps Roku's CPU or protocol offload ASIC is a bottleneck too?)
The recent Roku literature touts improved speed as one of the benefits of recent generation products. Roku can do a better job of living up to that promise by providing a 10/100/1000 full-duplex Ethernet port. NOTABLY, software updates can zoom down the wire. And, start-up buffering on channels can occur at higher rates (up to the limitations of the streaming service). And if the home has a local media server, the Roku can gain quicker access to it via a GigE connection to the home LAN.
Honestly, I didn't even know they made 10/100 chips any more. I know you guys pinch pennies (like the horrid cable company does with their set top boxes). But you really should spend a few more dollars and improve your hardware. Your whole model is based upon assembling a valuable customer base (that you can then use to justify demands for revenue split from the channels). If you lose customer base, you lose leverage with the channels. AND you will lose high-end customers if you don't provide better hardware in your top-end boxes. In some instances, we see better performance using the streaming client built-in to the TVset. Build a better top-end box.