I have been a web client subscriber for a while now and recently picked up a Roku. I was pleased to see a Roku Rdio client but not so with Rdio wanting to double subscription fees to allow me to use it.
I would have no problem paying a one time fee for the Roku app but charging an extra monthly subscription fee for what is functionally the same web service is not reasonable. If you are going to charge double the fee I expect double the service - as in two simultaneous connections to Rdio.
Mobile users get the benefit of offline access to music which justifies the extra fee but the Roku client does nothing like that, it is just a wrapper for the same web service.
Please reconsider your approach.