VPS issue. I suggest you contact Support.
You could force it with some trickery, but I think that would be out of scope for this board as it will only lead to confusion for regular copy/pastas (ie. like me, not on VPS) who might stumble across this thread due to it's subject title.
Again, allow me to reitterate that the notification you're seeing isn't necessarily a problem for Joomla! functionality, although I do understand that a "Warning!" looking sign in your admin section may give an unprofessional appearance or some cause for alarm, even though it's benign.
The Wiki article appears to indicate that the 'misleading' message doesn't show on Joomla! v1.5
Maximum Cash Discount on any plan with MAXCASH