Who is responsible for exit polls?

[Princess Turandot]

2. CNN has an explanation of this on their election results pages...

Several news agencies use Edison Research for exit polling, including AP, which many other news outlets use as their vote counter/winner projector. (The NYT, for example, doesn't show a race as called until AP does, which often is later than broadcast/cable news stations.)

Edison Research: To assist CNN in collecting and evaluating this information, CNN, the other television networks and The Associated Press have employed Edison Research. In previous elections, this firm has assisted CNN in projecting winners in state and national races. Edison will conduct exit polls, which ask voters their opinion on a variety of relevant issues, determine how they voted, and ask a number of demographic questions to allow analysis of voting patterns by group.
Using exit poll results, scientifically selected precincts, vote results from The AP, and a number of sophisticated analysis techniques, Edison also recommends projections of a winner for each race it covers.

On balance, the called 'winner' track record is far more accurate than not, otherwise they wouldn't be doing it, since it would make them look like idiots. The times that they're off in a high profile race are just more visible.

More at the link:
http://www.cnn.com/2016/01/30/politics/cnn-election-projections/index.html