Lists which force replies back to the list usually do so by setting the reply-to header to the list address. That makes it difficult to reply to the individual or CC their address when replying if that's necessary for some reason (e.g. if they're not subscribed to the list, but then allowing non-subscribed posts is another argument...) Even Reply All doesn't always include the original sender's address, since the reply-to header overrides the from header.
It's also possible that the sender might have set the reply-to header themselves to have replies sent to a different address, and by overwriting it the list removes that information. It is possible for the sender to force replies to their message back to the list, by setting reply-to to the list address; it's their option as the sender.
The mailing list sets the list-* headers (list-post etc.) so if your mail client supports it you can use the "Reply to List" feature. So you as recipient have a choice - Reply to the individual, Reply to List, or Reply All.
For what it's worth, the GIMP and Mozilla SeaMonkey lists also work in the same was as this list.
Mark.