Good interesting points so far to which I'd like to add my perspective as an airline pilot with relatively low experience (got taken on with 200hrs).
One of the things I found to be the hardest starting out on jets after training on piston engine light aircraft is descent management, i.e. you're at FL390, they want you at FL250 by such and such and then at FL150 and then you want to intercept the glide on a continuous descent so as to avoid levelling out and burning extra fuel but you also don't want to be to high because then you might be fast and long on the threshold etc. etc... Anyway, this is an example among others of aspects of airline flying which you do not really cover until you get into the airlines and no matter how many hours you spent drilling holes in the sky at 3000ft in Florida, you won't be able to practice it until you're sitting in that right hand seat.
I won't criticise the Americans' criteria for hiring because I don't know much about them beyond what's been said on this thread, but I resent what some say about how in Europe we hire pilots with low hours and it is supposedly unsafe. The aspect of airline flying I described in the previous paragraph is one among many that proove you can't learn everything flying light aircraft anyway. Happy landings to everyone,
G26