The way that drive manufacturers count size 1000MB is equal to 1GB. But software manufacturers and operating systems count storage as 1024MB is equal to 1GB. So when the drive is formatted it is recognised as a lower capacity than is actually advertised
This has been normal drive size listings for hard drives pretty much since the beginning of time. You don't have any issues. Unless this is your first computer I'm suprised you have not noticed this before.