Yes, you are right in this statement, but I do not want to write a long story. It seems that Ethash is only algorithm that is not suitable for FPGA.
Not so fast, there is a guy who claimed he can do Ethash at 421.41 MH (FPGA Nallatech 385A). I am still waiting for proof, so it may be possible. Or I may be waiting for a very long time.
https://github.com/Maetti79/OpenCL_FPGAhttps://github.com/Maetti79/ethminerThanks for the links. According to his latest results, the FPGA takes ETH hash from MEGA to GIGA.