Yeah, pretty much, though the full story is a little bit more complicated than that.

The reason a single short burn won't do it is that whenever you stop burning you will always be in an orbit that will return you to the point where you stopped (assuming you don't actually collide with the body you're orbiting of course). So you have to burn somewhere other than the orbit you want to get out of. The most efficient place to do that second burn is at apoapsis because that's where you get the greatest reduction in kinetic energy for a given delta-V (because that's where your velocity is the highest and so the force of burn is applied over a greater distance). But if all you have is a low-thrust engine (e.g. an ion drive) you can maneuver with long burns. The math gets hairier though.

Cool, thanks for the explanation. Looks like all that Kerbal Space Program was useful after all. :)