I assume you mean "specification grade". These receptacles cost maybe $3-4.00, or more each as opposed to $.89, depending on where yoy buy them. They have a deeper body and don't have push-in holes, although some can be backwired via the side screws clamping down on a pressure pad.
I've been told that the "spec" in spec house is short for speculation, rather than specification. Somewhere between a production home and a custom, these are built with the speculation that they can be sold for a bundle of $$ when completed. (This may or may not be true, please don't shoot me, I'm only the messenger)
Spec house may mean different things in different regions of the country.
Here in rural Nebraska a spec house is low grade housing where everything is built to code minimum. They are easy and fast, no extras, no questions about custom options. Margins are very thin, not much profit but if you need the work they can be better than nothing.