What is the technological reason that laser printers have declined in
retail price by 90% (from ~$1000 to ~$100) over the past five years? 
Is there a particular manufacturing means, such as use of LED strips
in place of the rotating mirror, that has allowed them to be made for
less?  Have key patents expired?  Are they making it all up in toner? 
Perhaps all of the above are true, but what I want to know is which
factor is the largest and primary reason.  I also want to know about
what percent of the sub $100 laser printers are using LED strips
instead of rotating mirrors.

"Last year the number of models tremendously increased. Besides, the
typical price range for such products is falling down: a year ago it
was $1000 - $1500, and now the price tags are often lower than $1,000.

Price-cutting goes along with some technological tricks aimed at
making the production cheaper. Some manufacturers save on interfaces,
memory, functions or software, others develop cheaper designs.

By the end of 2003 it was difficult to find a printer maker who
wouldn't offer color laser printers cheaper than $1,000. The market
hasn't formed completely yet and any company has a chance to get a
solid share. No one doubts that this market is profitable: just look
at the wide range of new models, sales at dumping prices and
price-cutting for existing products. Yet in summer several companies
announced sales of some of their models at $800, and by winter Konica
Minolta Printing Solutions trimmed the price for Magicolor 2300W to
$499 (in USA).  "
(source: http://www.digit-life.com/articles2/digests/itogiy2k3-print.html)

I'm not aware of any single technological factor (though I'm sure many
parts have gotten cheaper due to experience and economies of scale),
but there are a couple non-tech reasons:

1) Increased competition drives prices down and reduces profit margins

2) I understand that many printer companies are actually selling their
printers at a loss, and are making their profit on the sale of ink &
toner.