I suppose if you're telling the time with a sundial the o'clock would not only be redundent but incorrect.
As another example of idiosyncratic usage with regards to telling the time my mother always gives 9.25 as "five and twenty past nine" rather than "twenty five past nine".

I do wonder what the problem is that people have with variety in speech. If we can accept the vast number of synonyms that exist in english why is it difficult to accept that an 'otel and a hotel are simple variants. Personally I can live with, and enjoy, almost all of the variations of english.