I've had a pretty boring evening so I got to wondering, what's the most oft-photographed subfleet, as opposed to airframe, on this site? My unscientific research method has been to look up the number of photos in the index of that subfleet (answering the first part of my question,) and divide that by total aircraft operated (over all time, to save me time, and giving a measure of popularity amongst a.net photographers in general.)
My hunch was that KLM MD-11s are the most popular: 2,502 photos of only ten aircraft, or 250.2 shots per frame. This is the best I've found apart from the An-225's ratio of 544 photos to a single airplane, but it may be a case of confirmation bias. Concordes do well: 227 photos for each of BA's 7 and 131.1 for AF. Surprisingly, Northwest's a.net-legendary DC-9s aren't hugely well represented, at least by this method of counting: 2,308 photos total, but spread over 91 different aircraft (according to a probably-inaccurate planespotters.net list.) The best A380 count comes from Singapore Airlines: each of theirs averages 107 photos, with AIrbus' own examples coming in second at 104.
Still, my impression so far is KLM is incredibly well represented: their 747-400s score 147.2 photos and their 131.7 for 777-200s. Among Delta types, twin-aisle types are far more popular than boring old narrowbodies: 757-200s and MD-88s only measure 18.5 and 15 photos per airplane and the 767-300 just beats the 777 with 60.4 to the latter's 60. If nothing else, I hope this informs why your photo may have gotten a "common" rejection.
[Edited 2011-04-02 22:17:56]