Examples:
Tesco -> Tescos
Holiday -> hols
Final -> finals
Yes well, those are three completely different cases, aren't they:
(1) It's "Tesco's", not "Tescos", and it's short for "Tesco's shop". Now there isn't a Mr Tesco, but the usage is the same as saying "Blogg's" to be short for "Mr Blogg's shop".
(2) "Hols" is short for "holidays", no problem there.
(3) "Finals" is just wrong. (And I'm not sure I've ever noticed hearing it on the radio, actually.)