Nope, there are lots of acronyms that are usually pronounced by letter. FBI, CIA, GAO, DMV, and of course NPC. The definition of an acronym only requires that it be spelled with the initial letters of the words involved, not that it be pronounced one way or another.
Wrong on two counts: it requires that it be a word spelled with initial letters or parts of a series of words, such as RADAR (RAdio Detecting And Ranging) and Calvin's GROSS club (Get Rid Of Slimy girlS).
Actually, this is only one definition of acronym. The other (taken here from The Free On-line Dictionary of Computing) is: <jargon> An identifier formed from some of the letters (often the initials) of a phrase and used as an abbreviation.
Recognizing that the source is not the be-all and end-all of the English language, it is still noteworthy the word is here defined as an "identifier" and not as a "word," as in the primary definition. As an example, they cite the self-referential TLA which stands for "Three-Letter Acronym." Hard to pronounce that one.
Without this secondary definition, it would of course not be self-referential. This is neither here nor there, but borders on amusing.
I gotta be careful when sending subversive stuff like this, though. I think the fibby is monitoring my posts.
[EDIT] - Yes, AEL is an acronym. In fact, it stands for nine different things: http://www.acronymfinder.com/ af-query.asp?String=exact&Acronym=ael
Wrong on two counts: it requires that it be a word spelled with initial letters or parts of a series of words, such as RADAR (RAdio Detecting And Ranging) and Calvin's GROSS club (Get Rid Of Slimy girlS).
If it were called the Central Intelligence Agency Office, its initials would be CIAO, which is a word, and thus, an acronym. CIA, however, is not a word. How would it be pronounced? C-ya? Likewise, FBI is not a word... although fibby is, but I understand the agency doesn't like being referred to in those terms. NASA is pronounceable, and thus a word, and thus, an acronym.
The easy way to settle this dispute, though, is with common sense. My initials are AEL. Is that an acronym?