I think there is a need to differentiate between 2 forms of reply.
Namely the "Quote" form(currently within a message) and the "Reply" form(currently beside the [back]).
In a linear kind of forum, like phpBB, there is a need to really quote the message that you are responding to, especially when it is in the first few posts, otherwise, readers will have a hard time trying to figure out what tou are trying to say.
In our case though the message that you are responding to is not quoted(since your response will appear as a threaded reply), the "Quote" word let the user intuitively realise that by clicking "Quote" his response will be referenced to the message. "Quote" in our case merely means to cite the message.
If the "Quote" button is change to "Reply"(like Sphinx sugessted), there will be 2 "Reply" buttons. One used for referencing a message, the other used for replying to the main thread. This will cause confusion to the user.
"Quote" button should stay as "Quote" button, imply to cite the message.
Any thoughts? btw your votes counts