Exhibit A: There's two more in Anor Londo. This implies that there could be either a clan or entire race of these guys. So.....much like humans they're a dwindling race but perhaps even more than us. I mean, I still wish grievous harm to Rickert, but at least there's more than four humans kicking around. Additionally, they're segmented into groups with the two in the tower arena being isolated with nary a Giant or a Gwyndolin to keep them company. Sad indeed
Exhibit B: The two in the tower are well on their way to broken and dying. The first comes out gangbusters and can be said to be "whole." However, the second guy is missing his tail already and starts the battle with half life. Is the first guy just trying to protect his damaged buddy? Also, I've never seen the first one breathe fire. How did he lose that? I guess they're both banged up. But at least they have each other. Jimmy and Kimmy the Gargoyles have each others' backs and that's gotta be something.....
Exhibit C: Except that Jimmy and Kimmy have to stand guard over the best reason they're tragic figures in the game.....Timmy the Gargoyle. Have you ever noticed there's more than two gargoyles on that tower? How come only two attack? Timmy is dead and just hanging around up there.
Conclusion: You have three gargoyles isolated from what could be their home and society/brethren. All three of these show signs of deterioration ranging from a fairly insignificant limitation in power to a fairly major level of broke all the way to dead. So the existence of two Gargoyles is waiting to die (they're already starting to) while they sit next to a corpse of their buddy until the next "chosen" undead walks in to harass them.
Basically the Bell Tower is a Gargoyle Nursing Home and we just bust in and kick their walkers out from under them. Tragic!