Periods after abbreviations

[Damien Hall]

Jesse Sheidlower's signoff in his most recent message -

'Jesse Sheidlower, who thinks that "Ms" should not have a
period'

- has inspired me to ask about the following.  I think it
may be a simple transatlantic difference, but I'd be interested to know what
others think.

For me, prescriptively, if I might be so bold, no abbreviation should have a
period after it unless that period actually replaces letters, so correct forms
are:

Ms
Mr
Dr
Mrs
Miss

but

(Rt) Rev.
Prof.

However, I've noticed that universal usage in the States seems to be periods
after all of this type of abbreviation.

To confuse the picture further, in Britain at least the inclusion of the
'correct' period is coming more and more to be seen as too fussy and obscuring
'real meaning' at the expense of emphasising personal 'scholarliness' in the
worst sense.  Instead, in business communications, the tendency is towards
what's called 'open', ie 'no', punctuation, so:

Prof A N Other
St Agatha's College
OXBRIDGE
OE72 7YT
UK

28 Jun 2004

Dear Prof Other ...

British newspapers also follow this usage and don't, or rarely, put periods
after abbreviations of this type.  What's the difference between American
prescriptive and actual usage and British prescriptive and actual usage?

Damien Hall
University of Pennsylvania