SMD package sizes in Altium
I suspect that the reason for the different footprints is to allow for the different heights of different parts.

For example, a SMT ceramic capacitor is typically about as tall as it is wide. While a "typical" 0402 resistor I just looked up (here) is 0.5 mm wide, but only 0.35 mm tall.

Because the capacitor is taller, it needs a longer "toe" in its footprint to allow a good solder fillet to form (I haven't checked if this is actually what's different between Altium's resistor and capacitor footprints).

Altium's footprints are just a reasonable guess at good footprints for typical parts in each category (resistor, capacitor, inductor). To really optimize your design for high manufacturing yield, you should consider the actual height of each part number in your design, and account for your manufacturing process: for example, reflow and wave soldering have slightly different requirements for optimum pad sizes.