There is a distinction and it indeed gets a bit fuzzy. I.e. outputs bigger than 64?bytes (iirc) require extra allocations when writing to disk, but obviously that's no argument for prohibiting other types. A weaker reason with stronger (lol!) assumptions about its usage is that it should be theoretically spendable unless marked as such. Some script pubkeys might not be, which is a reason to only allow "types" that at least formally are.