The Monday Night Football crew did a good job of reminding viewers of the context of the record, even going as far as providing analysis showing how far above average both Marino's and Brees' were for their respective seasons. The NFL's passing numbers have steadily inflated over the years, largely due to rule changes that favor offenses. But like many other sports, it's possible that the athletes have simply improved over time. Defenders can improve too, but who's to say that athletic improvement on both sides of the ball doesn't disproportionately favor the offense. The fact is we simply have no way to tell.
We can use some statistical tools to get a feel for how outstanding each season was. Drawing the line at the top 30 passers in both seasons, we can calculate the number of standard deviations Marino and Brees stand above the season average. Marino's 1984 was 2.4 standard deviations above average, while Brees' 2011 (so far) is 1.9 standard deviations above average. Marino achieved his numbers on 564 attempts while Brees has 622 attempts, and counting. Brees has 13 interceptions compared to Marino's 17. According to PFR's Adjusted Net Yards Per Attempt, which factors in yards, attempts, interceptions, and touchdown passes, Marino beats Brees 8.9 to 8.0.
One of the unspoken assumptions when discussing Marino's 1984 record is that his record is a 'pure' or 'true' record, and the record set in 2011 is asterisked by the liberal passing rules of today's NFL. But do you know who's record he broke and when that was set? It was Dan Fouts in 1981. Before that the record belonged to...Fouts in 1980. And before that...Fouts in 1979. But prior that, the pro record was an AFL mark set by Joe Namath in 1967.
It's no coincidence that the record was set and reset in three consecutive years starting in 1979. The 1978 season was the first with modern passing rules. Most notably, contact with receivers was penalized beyond 5 yards and linemen were allowed to block with extended arms and open hands. That season was also the first lengthened from 14 to 16 regular season games. A record like 'total passing yards' is bound to be broken soon after those changes, and sure enough it was--repeatedly. The notion that the 1984 record was somehow pure or true, and the 2011 record is tainted due to rule changes is myopic in the extreme.
Marino was not a great quarterback because of his 1984 record--not at all, given that it was only 6 years after the tectonic changes of 1978. Marino was a great quarterback because he won games. But the fact that his record stood for 27 years despite more and more liberal passing is astonishing.