Newman 1974 lampoons newspaper use of the phrase marathon talks, placing it within a tradition of "the hack phrase, the labored point, and the stereotyped treatment" that runs through American journalism. The term certainly is well established, as the following examples will show. Whether it qualifies as a hack phrase, labored point, or stereotyped treatment is a question of individual judgment. Comparing the dates in the first example, one may justifiably see its use in that case, at least, as no exaggeration:
... marathon talks, begun in 1955, are continuing — Newsweek, 23 June 1958
... his voice hoarse from marathon speechmaking —Time, 24 Mar. 1952
... both Houses of Congress, neglecting all other business, held a marathon debate ... on the admission of Kansas into the Union —Morton Hunt, New Yorker, 3 Nov. 1956
This attributive use perhaps derives from the marathon dances of the 1920s or earlier; at least we have plenty of evidence for the attributive from that time:
Marathon bowling has generally fallen to the lot of the more ambitious male members of the bowling fraternity—Springfield (Mass.) Union, 8 June 1918
... what seems to have been a "Marathon talking test" in Hyde Park —Manchester Guardian Weekly, 19 June 1925
... Professor Camillo Baucia, "champion marathon pianist of Europe" —Time, 7 Dec. 1925
The Wolf is still-hunter or marathon chaser —Ernest Thompson Seton, Lives of Game Animals, 1925
The attributive is fully established and perfectly standard.
Howard 1977 is distressed by the misuse of the noun for an endurance contest of any kind. The original idea, he says, was to cover the ground as quickly as possible, and, to be sure, that is exactly what the best marathoners still try to do. However, Mr. Howard himself observed in another connection that "English grammar evolves with majestic disregard for the susceptibilities of classical scholars" (Weasel Words, 1978), and the observation is as true of vocabulary as of grammar. It is the notion of endurance—an obvious factor in so long a race—that has attached itself so prominently to the word in English, even in reference books:
... the marathon, the prize endurance event of the Olympics —Collier's Year Book, 1949
(资料出处：韦伯斯特英语用法词典)