Brass buttplates do dress up the Enfields and a link to the Royal Navy would be interesting. All rifles, regardless of the OEM or country of origin, are built with parts that have a specific purpose. Brass buttplates would be more expensive to produce when compared to steel or alloy buttplates but won't corrode when exposed to moisture or salt air.
There's something else that I noticed about Enfields. I've seen many of them for sale at gun shows and dealers with metal parts coated with a layer of black paint, mostly peeled. My own 1944 No. 4 Mk 1* Savage was painted although 90% or more was gone by the time I bought it several years ago. The 10 round mag had been painted but only the exposed portion. Obviously the purpose of the paint was to retard corrosion. Was that something that the factories did or was it a field modification?