[I'm a huge nginx fan myself but recall that this is coming to the main project soonish.]
It's like a sausage, you can enjoy eating it without seeing how it's made.
But apache can let you load a new .so without recompiling (or even restarting) the main server, which, for most intents and purposes, gives you equivalent functionality.
But I bet for developing modules, loading standalone is a huge help.
I haven't used nginx often, but the default Debian nginx doesn't come with many things included, I find.