Should we say that the space programs in the 60s and the 70s were more successful? specially, if we consider the communication and the control technologies available at that time. For example, vikings had Honeywell 24 bit cpu with 18K memory. What about those Argon computers used in the soviet venera programs?
Or may be, a very fast/accurate computation is not that necessary?
The landing techniques that are being used are bringing much larger payloads to the Martian surface than were brought in previous landings. Curiosity, for example, is about twice the weight of the Viking landers. In general, we're much more successful at landing and receiving data from mars-bound craft than we were back there; the soviets sent several probes to mars and got minimal data back from them before they failed.
Fast/accurate computing is needed for surface work on Mars because it means that the devices don't have to wait around for commands all the time. Giving more processor power and ability means that more flexible programs can be written to sift through the data and just send back the most interesting parts. Fast and accurate are very much needed for the kinds of lab experiments we're doing on mars.
Or may be, a very fast/accurate computation is not that necessary?