Dictionaries are intentionally not prescriptive. Style guides are, but few take them seriously as the entire concept of 'correct' English is considered stodgy, hopelessly old-fashioned and even (in extreme cases) prejudicial and stifling. It's even more outre and obscure than map-reading and GPS navigation, without the technological cachet.
If you've a love of 'good' English usage, let me recommend two books:
The Chicago Manual of Style, 15th Ed. - All you could ever want to know about usage, punctuation and a host of related subjects. An excellent desktop reference if writing is a pastime, profession or passion. Includes an excellent Glossary of Troublesome Expressions.
Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation - A humourous (it's a British book) look at punctuation use and abuse.
As an aside (and finally bringing this back on-topic), cache and cachet both derive from the French verb cacher, which means 'to press or hide'. The first meaning 'to press' came to relate to an official seal and thence became a mark of prestige, which is the sense of modern English cachet. Given the common origin, confusion is probably inevitable.