I've got a theory about why the Argentinians play there 7" records at 33.3rpm....
Many Jukeboxes (Seeburg in particular) played selections at 33.3 (Hence the 'Little LPs'/Motown EPs and U.S Jukebox 33s)... when the record companies realised that they were pressing up records for a small section of the U.S. market they probably decided that they could streamline their operations and only cut 7" at 45rpm - If this was the case there will have been tons of Jukeboxes in the U.S that were now defunkt...
I can imagine the tooling and any stock of theses Jukeboxes being passed off onto the nearest 'third world' country by U.S manufacturers.
If your an Argentine record company pressing up 33.3 rpms to supply to Bars, Pool Halls and the like, why bother pressing up 45s?
Dansettes, Sterograms and Gramaphones all play 33.3rpms so you're not losing any customers by not cutting 45s.
Could all be a load of nonsense though...