Is the main reason audio equipment depreciates so much is

all of the above, and not only in audio. depreciation seems fairly constant. I believe technology and parts quality does change, but not a fast as manufacturers want us to believe.

Yes, taters- from original cost to wholesale to middle man to full retail,
there is a tremendous mark-up.

Jafant,

When I am at a audio show and looking at a ton of gear I find myself trying to figure out what it cost to make the Item. Of course it's only a guess and I don't have actually numbers. I have worked in manufacturing before and I remember what it cost for us to make a product and then seeing the product on the open market. The company I worked for was owned by my sisters husband so I had inside information on what it cost to make an item. One popular item we made in the 80's and was distributed worldwide was a fashion Item. The parts came from China but the units were assembled in Southern California. The Item cost with parts and labor included was 7.00. The retail price was 69.95. So like you said about a 10 times markup from what it cost to it's retail price.

Not always true i had Mac  Mc275 and sold it for more than 4 times what i originally paid!!!

4. Overpriced.  

But this doesn't necessarily means that a good equipment should depreciates at ridiculous prices (a sad trend on Audiogon lately).  A well built equipment should give you years of enjoyment regardless of what you paid and its current worth.  

Just saying.