Every few years, our industry gets a new buzzword which becomes the “in” phrase. Remember ASSP, or application-specific standard product? That was a very useful and clear buzzword, but it never really caught on, unfortunately. This time around, I think it's “SoC”–the system-on-a-chip.
Everyone seems to be offering them. But there is nothing new about the SoC message; the entire history of the IC is about achieving higher levels of integration and putting more functions into a single device. To some extent, the phrase SoC is just an old concept with a new label. And what one engineer considers a “system,” another engineer may consider a subsystem–just as I have heard of a 19-inch rack-mount unit referred to as a “component”–which it is, though it's a lot bigger and complex than an IC!
What you consider a system depends on your perspective, just as a so-called “complete” IC usually also needs numerous passive components, voltage regulators, maybe an RF section, and some other peripheral functions. Check that data sheet carefully, and be sure the SoC phrase being tossed about is not just being used to get some glam with investors!