In-Place Hold: Is there a maximum percent of allowed mailboxes?

In-Place Hold has been advertised by Microsoft as a substitute for third-party journaling. To be effective as an archiving tool in most companies, In-Place Hold would have to be usable on all mailboxes.

I've read conflicting descriptions of In-Place Hold:

Various sources specify that ALL mailboxes (that have Hosted Exchange Plan 2) can be put on In-Place Hold.

However, this Microsoft website states that:

Each customer is allowed a maximum of fifteen (15) percent of all mailboxes to be on hold at one time.

(http://technet.microsoft.com/en-us/library/jj891031.aspx)

Which is true? Is there any Office 365 plan that allows ALL mailboxes to be put on In-Place Hold?