The price difference is only about $16 USD.
As far as I can tell, the Directron one has no fans. Plus, it only includes a 235W power supply by default, while the AMK includes a 300W power supply (Directron wants $25 to upgrade to a 300W). In addition, I would bet that the black case that AMK has is more expensive than the biege one that Directron has.
AMK does a bang-up job of doing case mods (I've got one of their big cases with 3 fans added)... if you want a cooler system, they've got quite a few nice mod options also.