[mkeung]

From my understanding, scrypt ASICs have been held back by the cost of memory hardware as scrypt requires more memory usage. There has been talk of forking existing scrypt currencies to require even more memory to counter ASICs further but so far I think only a few new coins have done this.

[jcampbell1]

My understanding is the scrypt currencies use the lowest possible memory factor, which was just stupid.

[tromp]

Its memory requirement of 128KB is a compromise between computation-hardness for the prover and verification efficiency for the verifier. You don't want verification of a proof-of-work to take a lot of resources, since every client has to perform it.