I know you can get to it using python, and it is quite useful, but is there any way to get that same data using the logic bricks?
No, there is no way.
The reason is simple: what should happen when there are two or more messages?
There are way too much options to process a body (and several bodies). The information you could get is if an message with a certain content was received. The filter by subject already does that.
I agree the API looks inconsistent, as you can set a body without any use (without using Python). I see it as simplification, when you have a lot of simple message senders, but just a few (more complex) listeners. I usually use the body when I have more information than the pure existence of a message (subject) can express.