Style of address on mailing lists / Anrede auf Mailingliste

I quote a mailing list message:

Deshalb ist es ja umso wichtiger, dass sich die Mitglieder ziemen und die entsprechenden Höflichkeitsformen und Ausdrucksweisen wahren, wie z.B. eine entsprechende Anrede überhaupt zu verfassen. (MM's emphasis)

Again and again I wonder: is it just in Germany that some lists expect you to write 'Liebe Forumsmitglieder' or some such, and are offended if you have no address at all?

I recall a UseNet group for some bookkeeping software where people wouldn't even reply if you didn't use a form of address. This was the case no matter if you were replying to an individual or writing a new question to the whole list (in the latter case, there is no really sensible form of address, is there?)

Here are some recent examples:

Liebe Kollegen und Kolleginnen Liebe KollegInnen Liebe / lieber X Hallo Frau /Herr X Hallo X Liebe KOUKO Liebe Liste Moin! Liebe Helfer Guten Abend Bonjour X Guten Morgen, X

I really can't understand why anyone should be offended if one of these is missing. And I believe a formal close is also expected. I have the feeling it isn't the case on English-language lists.