Point to disc collision doesn't seem like it would be significantly simpler than disc to disc collision. In both cases the most expensive computation is calcula

Point to disc collision doesn't seem like it would be significantly simpler than disc to disc collision. In both cases the most expensive computation is calculating the square distance between the objects, which can be done with a table lookup and an addition. In point to disc collision you then determine if the squared distance is less than the squared radius of the disc, in which case you have a collision. The only difference in disc-to-disc collision is that you compare to the square sum of both radii instead. Moreover, this kind of collision system is often used in games on systems where the hardware is capable of reporting pixel perfect sprite overlaps anyway, so I think you're on track when you say it's for dramatic effect. IME it's also frustrating in games where this isn't the case because you feel cheated when you die because a shot barely grazed some antenna.