Batwoman, Batwing, Batman Inc and Birds of Prey are books that stand completely apart from the others. They have a different tone, they have different characters, they have different purposes, they have different storytelling devices. They are in the Bat-universe, but they are VERY different.
The four Batman titles (Detective, Batman, Batman and Robin, Batman the Dark Knight) all have defined mission statements but are in the same basic boat as stuff like the Avengers titles. Ditto books like Nightwing and Batgirl, in my mind. All your basic street level unpowered hero working the streets.
They have those basic things in common, all of them, and I think a large portion of them are as homogenous as you say, but not the ones I mention above. Those are completely different in tone, and direction. Much moreso than, say, Secret Avengers vs Avengers, to say nothing of Avengers vs New Avengers (vs, I suppose, Avengers Assemble) which are almost indistinguishable. I read both titles (infrequently) and I can't tell you who is on what team or which is doing what, because it all blends together.
That's your opinion. But basically everything you have said about the Bat inspired books can be said about the Avengers. The underlying theme with each Bat inspired title is the same. Use deduction, skilled fighting, and some flashy gadgets to find and stop the bad guy. It's hard to see the difference in that as well.