@ Neil Stansbury
To answer your questions generally, the size was dictated by the requirement which was along the lines of the ability to deliver x aircraft sorties a day for y days in sea conditions up to a certain level. If you redesign an Invincible class CVS to do the same it ends up being pretty much the same size as CVF, CVS have appallingly low sortie generation rates as they were originally designed as an ASW helicopter carrier escort to proper carriers.
If you want to add catapults to a CVS you'd have all manor of problems, firstly actually fitting them in the thing as they're almost as long as the ship, reinforcing the deck which isn't up to the landing loads involved, which then means you have to increase the size of the ship to stop it capsizing, so again back to CVF size.
In other words the CVF delivers a lot more violence to the battle space than a CVS. To compare the USN Carriers in the Indian Ocean put more aircraft over Afghanistan on a daily basis than you can get on a CVS, or indeed the UK has parked in country.
@ Pete 2, the EMALS don't work on the aircraft itself, they're safely below decks and operate on a shuttle that penetrates the deck and hooks onto the nose wheel a la the steam catapult. The reduction in wear and tear is due to the progressive nature of the acceleration, as opposed to the kick in the pants steam delivers. My old man tells amusing stories of almost blacking out on launching from the old RN carriers as their short catapult length required a rather high initial kick.