Partially, another part of why we don't clock over 3GHz is because of the
Memory wall. Main Memory is still relatively very slow compared to the CPU, so increasing clock rate would not increase performance as the memory can't catch up. Also things like electron leakage, reduced chip life expectancy and yields become an issue.
If the rumoured specs are right, then Nintendo is continuing along the "efficient" system model, opposed to the generalised or brute force models MS and Sony have been following. The whole point to embedding main memory that close to the CPU to make thing more efficient by default and make programming easier since you don't have to optimize that portion of the code as much. The trade off is the RAM gets a lot more expensive for MB and there is a limit to how much you can have without prices going through the roof and having absurd chip sizes which would in turn lower chip yields. However it also means with each chip size revision, things get massively cheaper since most of the system shrinks with it.
I just hope that that isn't all the memory in the machine. Sure it would be efficient, but but you can't program away the lack of RAM.