So Obama bought a chunk of network time

[cacophony]

google to the rescue:

It is the closest thing in broadcast content regulation to the "golden rule." The equal time, or more accurately, the equal opportunity provision of the Communications Act requires radio and television stations and cable systems which originate their own programming to treat legally qualified political candidates equally when it comes to selling or giving away air time. Simply put, a station which sells or gives one minute to Candidate A must sell or give the same amount of time with the same audience potential to all other candidates for the particular office. However, a candidate who can not afford time does not receive free time unless his or her opponent is also given free time. Thus, even with the equal time law, a well funded campaign has a significant advantage in terms of broadcast exposure for the candidate.