Re^2:xxx means that the node is an answer to Re:xxx which is an answer to xxx. An answer to Re^2:xxx would be displayed as Re^3:xxx. You see the pattern?
Unless you are a bastard like me (and a few others), who believe "Re(garding):" is enough information for each level of reply, and who consistantly takes away the annoying "^\d" patterns (as a silent protest to horrible MUAs that started the "Re: Re: Re:..." subject prefix drama) ;-)
I have to say I dont really see the point in editing it out. It can be useful to see the depth of a node just by looking at its title. For instance 'Re^25:' is pretty suggestive of a thread that has gotten out of hand and might not be worth reading.