Why are dvds and movies typically released on the same day of the week
and why is that day Tuesday?  How long has this practice been
followed?

Hi jack70,
DVDs and Music CDs released on Tuesdays for several reasons.

Sales Figures are released on Monday[1,2]

Consumers know when to look for new releases[3]

If a Tuesday release is selling well, there still is time to order
more before the weekend.[3]

Shipments of music usually begin to arrive in stores on Thursday. That
gives the stores time to coordinate special midnight sales on Monday
evening, as opposed to Sunday, which is usually a shorter work day[3]

This practice appears to have been followed for 20 years[2,3]

Please let me know if you have anymore questions.

Thanks.

-googleexpert

References:
[1] http://ask.yahoo.com/ask/20040217.html: Why do record companies
release artist albums on Tuesdays?
[2] http://www.enquirer.com/editions/2002/10/14/tem_stupid14.html
[3] http://www.metajournalism.org/archives/000236.html
[4] http://www.digitalmediafx.com/Shrek/News/shrek-dvd-released.html
"When the LA Times pointed out that Tuesdays are an industry standard
for DVDs and Shrek was being released on a Friday"

I can't speak to DVD's, but movies are not released on Tuesdays.
Most are released on Fridays.  Some are released on Wednesdays,
to get a head start on the weekend -- usually smaller movies do that when the
studios know they're going to be trounced by blockbusters. 
 
There are industry calendars that list who's releasing what and when and
the studios all jockey with each other and claim certain days, particularly
around big holidays.  Sometimes 2 blockbusters are registered for the same date
and then there's a lot of huffing and puffing until eventually, one of 
the studios caves in and moves to another day.  Or another year!

The 2 films about President's daughters. . . the Mandy Moore one (I'm
blanking on the title) and the latest one with Katie Holmes, were both
supposed to open
last January on the same Friday.  Same plot, same everything.  Warner
Bros. vs 20th Century Fox.   Neither would budge.   Finally, Fox
backed down and moved its movie to this month.   And in the end, both
films were bombs.

As a retailer, it was my understanding that Tuesday was always the
"street date"[1] because it was the day of the week with the lowest
sales.

A list of music merchandisers and suppliers is on Yahoo[2] and the
National Association of Recording Merchandisers site.[3] To ask an
authorative souce, those would be a good start.

[1] http://www.cmpda.org/english/stdate.htm
[2] http://dir.yahoo.com/Business_and_Economy/Business_to_Business/Entertainment_and_Media_Production/Music/Distribution/
[3] http://www.narm.com/Content/NavigationMenu/About_NARM/Who_We_Are/What_is_NARM_.htm

I think the question was directed at DVD & VHS releases of movies, not
theatrical releases.