Who is responsible for selecting the type used for closed captioning?
(I don't have a digital set.) I cannot read the lower case e x t e n d
e d type often used, especially on "fast speak" shows like West Wing,
etc. I'd like to write to someone and ask why they don't use CAPS for
cc. (AND I JUST READ THE PREVIEW OF THIS--THAT'S THE TYPE THAT'S HARD
TO READ ON TV!)

If by closed captioning you mean captions (subtitles) that you can
turn on and off yourself using a caption/subtitle command, they are
generated by your television from text information transmitted as part
of the television signal. Therefore, the font used is dependent on
your television. If you find it difficult to read, try another
manufacturer's television. Most still use a variant of a bitmap font
from the 1980s, when microchips and memory capacity in televisions was
much more expensive.

Subtitles transmitted as in-vision text are generated by the programme maker. 

A special font has been developed for European digital television
subtitling, Tiresias Screenfont:
http://www.tiresias.org/fonts/screenfont.htm

There is a discussion of different captioning systems at:
http://www.joeclark.org/atypi/ATypInotes2003.html

He notes:

Nearly all the people who have specified fonts so far have been incompetent
They?ve also refused to learn over the decades 
There are no suitable fonts in existence

and on other pages on his site quotes:

Responsibility for these problems lies with the original North
American design engineers, who have admitted that font quality was
dictated by a desire to cut costs. If anything, the design of the
captioning typeface should have been paramount, since good typography
has everything to do with good captions, and if caption companies are
serious about their type, they will contract with typographic design
firms to design future generations of captioning typefaces. A good
example to follow is the British Broadcasting Corporation, whose
subtitling and captioning fonts, designed by the Department of
Typography at the University of Reading, are a paragon of legibility,
parsimony, and suitability for the medium.

and

Fonts remain a glaring oversight. 
  In developing the specs for built-in decoders, manufacturers
insisted on retaining the right to specify their own fonts. There?s
only one font per set, and it is decided upon by the maker of the set.
Every TV model can and often does offer a different font, and cheap
sets usually have worse fonts than expensive ones even within the same
brand name.


That site is very interesting if you are interested in captioning design.

Owain