That’s normal. For all flash/hard disk storage, there’s a roughly 7% difference between the manufacturer’s claimed capacity and what will actually be measured by the device it’s installed in. This is because manufacturers use the decimal definition of “gigabyte”, while electronics see things in binary terms. To the manufacturers, a gigabyte is 1,000,000,000 bytes (10^9), while computers etc. define it as 1,073,741,824 bytes (2^30). So 4,000,000,000 / 1,073,741,824 = 3.7252902984619140625, or ~3.72 GB. The remaining “missing” space is used by the system files etc.
This isn’t a new issue, by any means. Look on the box for any flash card or hard drive and you’ll see small print explicity stating the “1GB=1 billion bytes” thing.