I see your point griffon, but have you ever used cannons/artillery? As it is now, in open terrain they do their job, but for attacking cities, they are pretty much useless. With a stack of 15-20 artilleries you can expect to remove (a total of) 3-4 hp from units in cities, if you're lucky. I've regularly gone under streaks of 10+ bombardment failed, and more often than not the artilleries will kill the population (which is not entirely a bad thing) more than they kill the units.
To even things up, i upped the bombard values of all land bombard units by 4, and now i think it's a 50% hit - 50% miss ratio, which is suitable imho.
So unless they boost bombard values, you won't see only artilleries on the field, even more so that artilleries can't move more than 1 square per turn. Cavalry and tanks can't be replaced by artillery no matter what, cause they have huge mobility on their side.
Another thing. Ships battles have been fought from a distance for a very long time by bombardment now, so it would make sense to have bombardment ships battle.
Last thing, if you land on enemy territory and they have 30 planes, it doesn't make much of a difference if your units have 1hp or if they're dead by the air bombards
-corv-