It's not just that. "of" and "the" are often omitted from initialisms, possibly as a lingering effect of, and false transferral of the conventions from, Latin where "of" is just the genitive case and "the" does not exist.
"Rolling on the floor laughing" should properly be "ROTFL" but usually is "ROFL", and that example is nothing to do with Britain or the honours system. "Member of Parliament" is "MP" not "MOP". "Batchelor of Science" is not "BOSc." but is "BSc.". And so on.
I suspect that "Lord of the Rings" is only "LOTR" because the sort of people who use "ROTFL" are the sort of people who even read the appendices to Tolkein and got there first. (-:
