If you click safe only on danbooru or gelbooru, you'll be getting a lot more than ecchi.
However, we have some moments when a mod might not be on when a ton of pictures get uploaded.In these pictures might be something bad. We can't do anything about it until one of us hops on. (I'm usually asleep in the morning when it happens the most, so I can't get to them until I log on.) Doesn't mean that we aren't dedicated to removing it.
We're given our rules on the pictures. Some of us might take them at face value, which means some things you might consider ecchi, but are technically safe.
I go by google's standards (And other mods may as well) for their image deletion. It's very strict, so I rarely let anything ecchi through. If it does follow the rules but still looks ecchi, I might still delete it under the fact that I can label it questionable.