My 2 cents (Score 1)

Any attempt at suing them will fail simply because of the way RISC OS works. Its highly modular, to the point that users can effectively dynamically substitute bits of the OS whilst it runs. This means what they've done is most likely only creating programs that run on the system. In order to not violate the GPL they simply point you to the original source. Its no different from compiling a GPL app under RO and running it.