My 2 are housecats and are not in the slightest bit bothered. We don't have a garden but they do go out on the balcony when they want to. One is epileptic so even if I decided to make them outdoor cats, he would still need to stay in. He'd be far too vulnerable out on his own.
My two were indoor cats when I got them - they were 18 months old - and it suited me as I live in a city centre. I think that if they have always been indoor cats they know no different.
My flat is big and on two floors - they hare around trying to murder each other and generally doing normal 'cat stuff'. They will be 7 in June (29th June if my little brother reads this).
I couldn't keep my two Houdinis in if I try!!! They are true escapologists! And love the outdoors! Watching birds, chasing each other, climbing trees and catching mice! Never had a house cat! Though they do worry me when they wander too far and I lock them in each night away from foxes as they have both been chased!