The number and places where sellers and presumptive buyers / users can meet have greatly increased. More and more, the recipient is under control where, when and what he want to 'see'.
And most the time the Seller knows more about his potential 'buyer', than the traditional publishers and can choose among many different 'distribution channel'.
Ross Mayfield calls it (in 2004) the "transitive advertising model", John Battelle the "sell side advertising" and Kevin Kelly prefers the term "choice ads" ... but it is by no means about the name.
It is about the rejuvenation of ad business, where advertising is relevant (and/or entertaining) for the recipient and send sender and both have the chance to "talk" about something "important" (at a given time).
Kevin's Ad Model Matrix
Source: kk ct2
Kevin Kelly article - recommended read
'A New Corner in the Future of Advertising'