Tables involved in replication need at least one uniqueidentifier column. If you don't have such a column one will be provided for you. Actually, it's slightly more complicated than that. Transactional and snapshot publications that allow updateable subscriptions require this column (and, I think, the "MSrepl_tran_version" column name). Merge subscriptions also require a row identifier column. Basically, this column is used to track changes to the replicated data. BOL has some, occasionally contradictory, information on this field, but not a whole lot.
My experience with non-updating transactional replication is that you get this column whether you like it or not. We stopped doing replication a little over a year ago and I'm still weeding these out of my database.