That's actually about right. The Roboard's USB speed is significantly lower than a regular PC or netbook. The 110 had improved this from the 100 a bit but not in comparison to other devices.
Having said that, if you are using a remote desktop app as apposed to a directly connected screen try slowing down the preview rate (Options button->Other->Max Preview).
Also, if you have not already, try pointing the camera directly at a light source to see if that increases the frame rate. Many cameras will really slow down with low lighting so pointing at a light bulb should give it enough light to go full speed. If that's the case you will have to increase the shutter speed which will darken the image and then use the Color Balance module to pull the intensity back up to normal viewing. Or you can get another webcam that does better in lower lighting.
Another point would be to experiment with the data format that the camera sends back. If you pull up Options button->Video tab->Video format check what data format is used. RGB24 will transmit 3 bytes per pixel, RGB16 will transmit 2. So by selecting another format can decrease the amount of data being sent by the camera which means the USB speed limitation is not as bad. This can really help to improve overally fps while sacrificing a bit of color and/or intensity resolution which is not needed for many applications.
You can also verify that RR is doing something funky by trying another capture application like AmCap that will give you another data point to compare with.
Let me know if any of those work.