In my opinion, the current wording in the HTML footer encourages bad mailing list etiquette.
The names of the links "Reply To Group" and "Reply To Sender" imply that clicking them will cause a reply to be sent to either the group or the original sender. In reality, clicking those links cause a NEW e-mail to be sent (not a reply).
It is most usual for a "reply" to quote the original message. When you reply privately to the sender, you typically want to quote at least part of the original message. The same applies to replying to the group: it is counter-productive if members send messages to the group as if they are "replies", but without quoting anything of the original message.
There are several good reasons for quoting when replying: not all mails arrive in the correct order at the recipient; message rules may sort mails into folders that do not contain the original message; when replying to a message that make several points, it is preferable to quote the points that you reply to; if a reply is a one-liner, you don't want users to have to consult previous messages to understand the post.
Yes, the two links in the footer does attempt to retain the subject line, but IMO retaining the subject line is of secondary importance. In fact, I truly don't care if users do or do not use the same or similar subject line for replies, as long as they quote relevant sections of messages that they reply to. (This may be different for groups where threading by "topic" is more important.)
Instead of "Reply To Group" and "Reply To Sender", rather write "E-mail To Group" and "E-mail To Sender". Or better yet: "Group's address" and "Sender's address". But I understand that it is sometimes considered "good UI design" to use actions/verbs as link labels.
In fact, if I was able to modify the footer (I understand why I'm not), I would get rid of "Reply To Group" altogether, for it serves a purpose very similar to "New Topic", and surely most mail programs have a REPLY button! Having the sender's e-mail address in the footer is very useful, though (to encourage private thank-you messages).