I need specific data that can prove / show companies in these
industries that they need the Internet.  Also, what the Internet (a
web site) can do for their business.  This information is going to be
used in sales and marketing materials for a small web development
company.

There is three levels of research / information.  

General ? Example: 80% of households that make more than $50,000 have
internet access.

Industry Specific - Example: Three out of four people use the internet
for making health care decisions

Detailed Specialty - Example: Physical therapists are 5 times more
likely to need web site then other medical practitioners.

We?re looking for information at level 3 for the following business types.  

- Chiropractors
- Podiatrists
- Dermatologists
- Ophthalmologists
- Physical Therapy
- Nursing Homes
- Developments
- Law Firms
- Travel Agents
- Event Facilities i.e. Banquet Facilities / Golf Courses

It's understood that this level of information may not be available
for all industries listed.  In which case I'll accept information on 5
as a completed answer.  A tip will be provided for answers on more
than 5.

SmrtMoney,
I'm afraid that the information you need for level three will be too
speculative for any source to accurately supply. The exception to this
would be if any of those industries had a central licensing or
governing body of which all members had to report their sites.

The best source to find the information you're looking for, without
commissioning a very extensive survey... 
http://clickz.com/showPage.html?page=stats

Having marketed to some of the industries you've mentioned previously,
my suggestion would be to use verifiable data from sources like ClickZ
or Nielsen/Netratings (www.NetRatings.com) or PewResearchCenter
www.PewResearch.Org for your level one and two. For the level
three/detail - the most effective means would be to be to perform your
own survey within a specific geographical area or cite examples of
other in the specific industry's Website. ie: Show a chiropractor
another local chiropractor's site, if there are no comps.. look to a
larger locale and larger operation.

Sorry it's not the answer you're looking for, but hope it helps. Will
let you decide if it's worth anything, or suggest a token donation to
a local charity.

Best of Success!
- Doc