The larger issue is that there are different encryption algorithms used for both currencies:
bitcoin uses SHA-256
and litecion uses scrypt

Both algorithms have different properties.

SHA-256 requires very few memory, it basically can be designed as a set of logic gates. This can be done very easily in a FPGA or ASIC.

Scrypt on the other hand needs a lot of memory, which makes current FPGA or ASIC boards practically not usabe usable for this kind of algorithms.

So at the moment there is not known implementation of scrypt for FPGA/ASIC and it's quite unlikely that one will appear in near future.