I'd like to know why the envelope you get to return your payment in
the mail for just about every bill I've ever seen has a "glassine"
window for the return address instead of just having the return
address printed on the outside of the envelope.  This means that you
have to insert the payment coupon correctly or else the address will
not show through.

Hi segwonk,

Interesting question! From the business's point of view, using
envelopes with windows avoids duplication (printing the address on
envelopes or address stickers in addition to printing it on the bill),
reduces errors and saves money:
The "envelopes have a glassine window so that the addressee's name
will show through. Thus, the person's name and address, on
correspondence or a document, can be used as the mailing address,
which avoids duplication of effort, reduces errors, and saves money."
Runestone Graphics, LLC
http://www.runestonegraphics.com/selecting_envelopes.htm

Environmental concerns:
Plastic (Polystyrene films) versus glassine windows:
http://www.eya.ca/steplightly/glassine.htm

Glassine Running Tips:
http://www.multi-plastics.com/PDF%20files/Glassine%20Running%20Tips.PDF

Tools & Tips:
http://www.supportsys.net/env_window.htm

I hope this helps - if you have any questions or if I haven't
satisfied your request, please post a clarification before rating my
answer.

Thank you,
hummer

Search Strategy:
://www.google.ca/search?as_q=envelopes+glassine+window&num=100&hl=en&ie=UTF-8&oe=UTF-8&btnG=Google+Search&as_epq=&as_oq=&as_eq=&lr=&as_ft=i&as_filetype=&as_qdr=all&as_occt=any&as_dt=i&as_sitesearch=&safe=images

Terms Used:
envelopes 
glassine 
window

An additional reason is that they can order envelopes in huge
quanitities and don't have to worry about them becoming obsolete
should their address chang.  Also, if they are a company that has many
offices, the same (bulk purchased) envelopes can be used for all
offices.

Not personalising the envelope simplifies the automatic processing of
outbound mail where bills for different companies are printed and
mailed by a third-party mailing house, or where the address to where
the payment is to be sent varies according to the type of bill or
customer. A company might have a central printing/mailing centre
(because of the high cost of the machinery), but several regional
offices for receiving payments and dealing with customer enquiries,
for example.

Owain

Another reason: Incoming envelopes can be mechanically oriented to be
facing the same way and then run through a slitter and the contents
removed. At that point, all of the remittance advices are ALSO
oriented the same way, so they can easily be run through a scanner.
Otherwise, most of the remittance advices will have to be spun 180
degrees, or flipped over, or both.

Hello segwonk,

Thank you for the nice rating and unexpected tip, I appreciate both. 

Sincerely,
hummer