The House of Bishops includes Diocesean Ordinaries (the head bishop of a Diocese), Suffragan Bishops (the Bishop who'll take over as Ordinary when the Ordinary retires), and Associate/Assistant Bishops (no right of succession, but they help the Ordinary with his/her duties). Only the Ordinary has jurisdiction in their diocese to approve/deny liturgical changes such as celebrations of same-sex unions. The rest were there at the HOB, though, so this wording was used.
It's Co-Adjutors that take over when the Ordinary retires. Suffragans get to share admin duties but don't have jurisdiction. I believe at GC2003, there was a vote to amend the canons to give voice and seat to ALL bishops--suffragans and assisting. I believe it was defeated, but has to be voted on a second time according to sacred canons. I'll have to go back and re-read the journal (if I can stomach it, that is).