When my house was built in 2001 we had the plumbing company to rough in basement bathroom drains. We knew that this would help us whenever we got around to finishing the basement as we didn't want to have to break up any concrete to do this. They told us they are tied into the septic system so all we needed to do was connect the supply lines and attach the fixtures to the drains.
As you can see from the photos, the toilet drain pipe is easily understood as is the sink drain. The shower drain is inside the cinder block in the concrete, but the additional pipe stubbed up inside of the wall is what I'm not sure of. Could this possibly be for the vent? If so, could this be the vent for all three fixtures? (or am I being too hopeful here)
Since the pipes are beneath the concrete I really have no way to tell for sure, but I'm hopeful that you plumbing experts can tell me what this is and is this the normal (industry standard) for doing a roughed in basement bath.
2" pipe circled looks like it's the toilet vent if I had to guess. The 1-1/2" coming up out of the ground is the vent for your tub/shower. The other drain for your sink will have its own vent when you cut a tee in for the trap arm.