Because no other base brings up the past even nearly as much as Britney fans. Furthermore, with them it's the very DISTANT past, the relatively short window of time in which she was on top (99-03).
As far as the Gaga comparison goes, 2009 is not the distant past at all, and they don't mention it nearly as often as BOMT or OIDIA get mentioned. Beyonce fans don't mention DC that much either, (ya'll don't let us), and the Katy point was just
![skull](http://img.photobucket.com/albums/v232/korn0818/ATRL_Smilies_All/faces/skull_zpsksni5fmm.gif)
In short, no other base brings up these ancient receipts even half as much as the Army.
The only ones you
kinda have a point on is the Mariah and Madonna comparisons, but here's the difference: They are in their mid-40s and 50s respectively, barely releasing current music and simply aren't 'current' pop girls, like Britney is. It is natural that their past receipts (not over a 4 year span, but 16/however long between Madonna's first and last smash eras) are what we fans discuss for the most part. Furthermore, we Lambs tend to keep it in the base, rather than opening up 16543457678 threads comparing Music Box or Daydream to current releases in a much different sales climate, or opening up "why don't ya'll talk more about Mariah's smash eras?" threads like I've seen for Britney.