For over a decade prophets have voiced the contention that the organization of a single computer has reached its limits and that truly significant advances can be made only by interconnection of a multiplicity of computers in such a manner as to permit co-operative solution...T he nature of this overhead (in parallelism) appears to be sequential so that it is unlikely to be amenable to parallel processing techniques. Overhead alone would then place an upper limit on throughput of five to seven times the sequential processing rate, even if the housekeeping were done in a separate processor...At any point in time it is difficult to foresee how the previous bottlenecks in a sequential computer will be effectively overcome.

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Compairing Apples and Oranges

1. The parallel code is not the same as the single process/thread code -- Fewer processes/threads per processor
    
   
2. In distributed systems there can be reduced overhead. -- Fewer processes/threads per processor
    
   
3. It is almost always the case that cache/memory size is effectively increased -- reduced reliance on swap/disk space
   
4. 
   At its core Amdahl's Law does capture a distributed systems reality.