Our datacenter is strict with them and requires us to justify all IP address assignments before asking for more. Our datacenter is strict because they get their IP addresses from ARIN and there is a limited supply.

Think of it this way:

No one "owns" an IP address in the same way we might own a computer or a loaf of bread. IP addresses are assigned by a central authority in groups to various regional authorities (ARIN in North America, AfriNic in Africa, RIPE in Europe, etc). These regional authorities are responsible for managing large blocks of IP addresses and assigning them to larger-scale network operators (the backbones of the Internet).

From there, smaller and smaller blocks are delegated to other network operators and hosting companies leasing space and service at each level of this hierarchy. Back at the top, the Regional authorities have to make sure they have enough IP addresses, so before they assign another large block to a network operator, they require justification to ensure that the IP addresses will be used and delegated properly. So the network operator then requires a justification from their customers before assigning the smaller block, and so on. 

A Small Orange has to provide justification for each IP address it assigns before we can ask for more from our datacenter. Using SSL is a proper justification. There are others valid reasons as well, but for the average website there is usually no need for a dedicated IP address unless it is using SSL Certificates.