[noobiscus]

You've appeared to miss the fact that the OED lists as definition 1 the COMMON usage, and further definitions are LESS USED.

Ergo; using an uncommon usage, you have to accept that many people won't understand you. Creating understanding is the essence of effective communication :)

[c0riander]

Actually, you may be interested to know the OED is a historical dictionary and in fact does not necessarily list common usage first.

  The OED is a historical dictionary, with a structure that is very different from 
  that of a dictionary of current English such as ODO... For each word in the OED, 
  on the other hand, the senses are dealt with in chronological order 
  according to the quotation evidence. This way the senses with the earliest 
  quotations appear first, and the senses which have developed more recently appear 
  further down the entry – like a ‘family tree’ for each word.

http://oxforddictionaries.com/words/the-oxford-english-dicti...

Not to mention, those familiar enough with the word to understand what Apocrypha are should hopefully be able to infer why someone may be referring to apocrypha without a capital A. It's not a long cognitive leap.

If you're suggesting that a number of people may not actually understand how to interpret or use the word, then I agree (as in this thread, I suspect). But that is the case for many descriptive and useful words in the English language and has rarely been a good argument for dumbing down the level of communication.