With the season just ending, we've had exactly 3 QBs throwing for 4,000 yards or more.
At this point I will remind everyone that [b]Danny McManus holds the record of 8 consecutive 4,000 yard seasons /b. This was an amazing feat of consistency and endurance, since missing even a few games in any of those seasons would have made it that much harder to reach 4,000.
Here's some number crunching to put this in perspective:

Since 1999, there has been an average of just under 4 QBs hitting this threshold each year  with a peak of 6 in 2000 and a low of 2 in 2001.

Let's suppose that in any given year, each of the 8 or 9 starting QBs has a 50% chance of being one of the guys that surpasses 4,000 yards. That means the odds of doing it two years in a row are 25%, three years in a row 12.5%, etc. And the odds of hitting that mark for 8 consecutive seasons are 0.4%.

In 11 years as a starter, McManus had a total of 9 seasons with 4,000 yards or greater. In comparison, the combined total of all the current starting QBs from the four western conference teams is 10. The combined total from the four starting QBs in the east (which includes Allen and Calvillo, and their combined 35 seasons) is 12.
However you slice it and whatever you think of Danny as a player, it is undeniable that this record is pretty impressive. I don't think it ever got mentioned often enough, in comparison to, say, the string of consecutive 1,000yard seasons by Terry Vaughn or even Kelvin Anderson.
Hats off to Danny!