On my TS-7800 [1] which has GigE and a 500MHz (!) CPU, Samba outperforms the Raspberry Pi (15MB/s vs 7MB/s). Note that on the RPi not even the whole 100Mb link is utilized despite the CPU being slightly faster in general (yes, I did some benchmarks) - and the CPU on the TS-7800 was actually designed for storage applications. So there may be something on to your claim, and it would appear that CPUs that include graphics and stuff are not that good at I/O.

[1] http://www.embeddedarm.com/products/board-detail.php?product...