Like the others said, it is probably just the way the company ordered the phones from BB. As long as the phone works and there is no issue, I wouldn't be inclined to think of it as fake.
If you want an OEM case, you could get one of the similar ones from third party sellers. Personally I would look at blackberry bold accessories
, but there are other sites that sell OEM cases and look-a-likes as well for less then if you ordered one straight from RIM.
Hope you enjoy your new phone!