What's so special about this FPGA that it can mine anything other than a sha256(sha256()) coin?
A Field Programmable Gate Array (FPGA) can be reprogrammed into doing almost anything you want it to do. If the printed circuit board around it doesn't support your new application, you can still re-use the FPGA.
An Application Specific Integrated Circuit (ASIC) is locked into doing only one thing. It's not field programmable.
So yeah, an FPGA miner probably has higher reuse value than an ASIC.
But that's not something the average customer can do is it? So retail value won't be that much better.
... and, as an example, they'd need to add RAM to it to be able to design and run scrypt mining (litecoin)
... and it's not just go to your local shop and buy some RAM either ...
sha256 uses hardly any memory - it's very different to most other applications in more than one way
The biggest one, in BTC's use of it, is that it needs to do 4 billion iterations to find 0 or more (average 1) results on almost the same data set.
The input (and output) is very simple and very small compared to the work done.