Most satellites are still simple "bent-pipe" kind, send data up in one frequency, translate, send it down in another frequency.
Boeing SDC (formerly Hughes Space and Comm) was (and probably still is) the leading company in DSP payloads and only one with the expertise to space qualify an IBM ASIC, but they have a broken business model and a hard time selling it to their customers. That and they have a very out-dated bus led to market deterioration over the years.
That aside, bigger satellites are just like bigger processors: it will become prohibitively expensive to develop and produce at some point. DARPA has been funding research in microsats with absolutely no redundancy and minimal radiation shielding, so you can build a Beowulf cluster with graceful degradation and a giant transmission relay (like TDRSS)