The usual 'binary' scale goes like this: 1 kB = 1024 B, 1 MB = 1024 * 1024 B, 1 GB = 1024 * 1024 * 1024 B, etc. which may be at odds with SI but at least it's self-consistent. The page you've quoted seems to be suggesting that 1 KB = 1024 B, 1 MB = 1024 * 1024 B, and 1 GB = 1000 * 1024 * 1024 B. That seems pretty absurd to me, but maybe they're just taking a page from the book of the "1.44 MB" floppy disks which actually hold 1000 * 1024 B.
My point is it's a mess and it's unreasonable to claim proper rules are followed.
E.g. how do you measure hosting bandwidth? A random calculator (http://www.ibdhost.com/help/bandwidth/) says:
1KB = 1024B; therefore, 500MB = 512000KB = 524288000B .. and .. 1GB = 1048576000B