Why USB or HDD Showing Less Capacity Than Advertised

Why capacity is always less than Advertize?

If you notice that all of the USB, not only USB all kinds of storage including HDD, Portable HDD, SSD, Memory cards, USB Flash Drive or any other storage media always shows less than the written or advertized capacity but did you know why it is less than the advertize capacity? Here is the storage calculation. Hope after reading this you will be clear about your question why 8GB USB showing less than 7.5GB and is it normal or abnormal-

Not really big as advertize
Not really big as advertize

Storage Conversation Method:

As per the HDD/Flash Storage Manufacturer: 

1GB= 1000 MB= 1000 x 1000 KB= 1000 x 1000 x 1000 Byte= 1000000000 Byte

As per the Programmer/ Machine Language: 

1GB= 1024 MB= 1024 x 1024 KB= 1024 x 1024 x 1024 Byte= 1073741824 Byte
So, 8GB= (8 x 1000000000)/ 1073741824
             = 7.4505 GB equals to 7.45 GB
           8GB= 7.45 GB
And for 4GB if we applied the same method we will found it as 3.725 GB. This calculation can be applied for any other capacity even for 500GB HDD or 4TB HDD. This is standard method of calculation of the Storage. This is the only reason for that physically we found less capacity than it is advertize by the manufacturer as attached picture. As a end user we are loosing a huge numbers of capacity but we are paying for that, did you ever think about that?