I believe that your understanding of orbital dynamics is perhaps a bit off. Yes, the projectile will return to its original point of departure, but (and this is the key) the Earth won't be there anymore, as it is moving as well. That is the whole point of orbital velocity, the projectile is moving fast enough RELATIVE to the point of departure, that their orbits are 'coordinated' (more precisely, they are moving relative to one another, in a stable relationship), and hence in a stable or quasi-stable relationship. In point of fact, it IS all about velocity, since the satellite doesn't 'know' what imparted its delta-vee
A launch from a cannon, electromagnetic catapult, BIG trampoline, rocket, what-have-you all show the same behavior, and all have the same requirements. A satellite lauched from a rocket makes secondary delta-vee changes during flight to alter its orbital path, but it need not do so. Yes, a course correction is often desirable to provide some orbital paths, but there is no necessity that this be done. Satellites, I might point out, often have highly elliptical orbits (the Soviets did this with communications satellites for years, as circular obits were poor choices since their country lay so far to the north), but even circular orbits can be obtained by arranging for the originally elliptical orbit to brush the top of the atmosphere (yes, I know...terrible imagery), which would slowly adjust the orbit to become less elliptical with time. This technique was used with several of the problems sent to Mars (the Odyssey, for instance), to minimize the fuel necessary to bring along....