Yes but that's ammo not the added level of protection for the ammo. CASE doesn't change what it protects. What happens if the weapon gets upgraded? Multiple tons of ammo? Uses alternative ammo? .5 tons per ton of ammo instead .5 tons for all the ammo in the location is a lot easier.
I can see the benefit of doing it this way - each round being protected means the vehicle does not need to be refitted to use the protection. (Just the loading mechanisms to remove the protective shrouds from each bit of ammo). Depending on the autocannon (or missile) ammo loading, the protective system would protect an entire 'shot' of ammo, rather than individual rounds (i.e. an LRM-20 will have each packet of 20 rounds protected, rather than each LRM).
Mathematically it is identical:
Half as many shots per ton for individual round protection
vs
one ton of protection for every ton of ammo
For smaller vehicles with only one ton of ammo this would be a useful modification as they do not have the tonnage for a full one-ton protective setup. You just need to have enough technicians back at the base to load the ammunition into the protective containers so the vehicle can be reloaded properly.
I could even see this extra protection being useful for longer periods, as a vehicle with two tons of protected ammo can get hit in either of the two tons with minimal worries. A vehicle with 1 ton of ammo and 1 ton of protective equipment might get hit in the protective equipment, ruining that protection (and potentially preventing that ammo from being used). However, in a strategic game that extra protective equipment is the predecessor to the "1 ton protection for all the ammo" -> "CASE". The protective sleeve for reach round/clip is a relatively dead-end technology, where further advancements only increase the percentage of each ton of ammo that is actually ammo instead of protective sleeves.