They do address this in the doc, Orgs can now (although it was vague as to whether it was an option or just the new standard, probably option due to business contracts) 'pool' the Usage billing across all users.
I'm guessing they did that (and the 'temporary bonus credits') to make the pill easier to swallow for that side of customers.
For orgs, each user was allotted their own quota. For messages beyond that quota, a pooled budget is available.
You're right, I missed that.
It still does make one wonder, why have seats at all though? If everyone is just in one big API credit pool - what do the seats/users accomplish?