The short answer is: a shock is just a damping mechanism that keeps the suspension from oscillating at one of its resonant frequencies; a strut is a shock (possibly with an integrated coilover spring), that becomes an integral part of the suspension. A good history and description is at ukcar.com.

http://www.ukcar.com/features/tech/suspension/mac.htm

Tim

 

Yeah, look at some aftermarket coilovers for an S2000. They are moderately beefy but not huge. Then look at coilovers for the front of a WRX. They are absolutely massive. The reason is they are struts, and have to support all kinds of different loads on them, such as lateral g's, back and forth loads, as well as up and down. S2000 shock only has to deal with the compressive forces acting on it, therefore it can be much smaller.

 

A shock is the reaction you have to a man with a big floppy hat and a purple suit (struttin').