Apparently, Target’s POS terminals are networked.
Here’s the analysis of the malware, and from that you can clearly see that the terminal must be running Windows and be capable of connecting to the internet:
http://krebsonsecurity.com/wp-content/uploads/2014/01/POSWDS-ThreatExpert-Report.pdf
I was thinking that everyone certainly is speaking negatively of Target’s system until I suddenly remembered that POS also means “point of sale”.