The deal between Vendors such as Microsoft and resellers are pretty complicated to understand... I really can not claims to be able to explain it... What I do read is that Mi icrosoft expects the majority of partners to buy Office 365 via the 2-Tier distributor arrangement, rather than 1 tier partners due to the billing flexibility etc.
http://www.crn.com.au/News/402625,resellers-to-get-office-365-on-monthly-billing-via-disties.aspx