Lack of paragraph spacing in newsletter emails in 5.0.1

[Graham Stoney]

I've just upgraded to 5.0.1 (thanks Andre!), and noticed that the
spacing between paragraphs in newsletter emails disappeared in the
TwentyTen MailPress theme when viewed in Outlook Express 6.

This appears to be due to the addition of this line to style.css in
the theme directory:

p {margin:0;}

The fix is to delete that line; but I'm wondering why it was
introduced?

Cheers,
Graham