To be "glad of" or "glad about"? [closed]

I was wondering about the correct usage of the term "glad". It seems to me it can be used (at least) in two different ways: "to be glad of something" or "to be glad about something", indeed I found both of them in some online dictionaries. But I cannot really understand what is the difference (if there is any), or if one of the two is more correct than the other.

Thank you very much for your help!

glad of something : - grateful for something

glad about something : - pleased; happy

Oxford Advanced Learner's Dictionary

Does it not boil down to the difference in meaning between 'of' and 'about'? The dichotomy raised not only applies to 'glad'. It could equally apply to 'envious','sick', or no doubt countless other adverbs used to qualify the verb 'to be'. In English prepositions are largely determined by usage, and can differ according to place or region. Americans always seem to me to be using the wrong prepositions. E.g. they will say 'different from' (Mike is different from Bill), when surely English English demands that you say 'different to' (Jenny is different to Jane). I would tend to say that I would be 'glad of a cup of tea' meaning I would like one. But I might be 'glad about the fact that tea was available'.