I don't follow that conversation at all. In the first part where you keep talking about "they." I can't even figure out what "they" are supposed to be. And in the second part again, I don't understand what you are trying to calculate, you didn't post the beginning of the exchange. How long would what take? None of that makes any sense.
DVD's are not 4.27 GB using any counting system. They're listed at 4.7GB (4.7 billion bytes) by marketing, but that's decimal. However Windows calculates storage capacity in binary, so the useable capacity is 4.37GiB (binary) in Windows. To convert decimal to binary, you have to divide the decimal value by 1.024 for every full digit grouping. 4.7GB (4,700,000,000 bytes) has 3 full digit groupings, so you divide 4.7 by 1.024 3 times and end up with 4.37 binary GB's.
Hard drives are not binary or decimal, they simply contain X number of 512 byte sectors for their total capacity. What determines whether their capacity is given in binary or decimal, is solely based on who is calculating the capacity. All MS based operating systems and basically all other mainstream OS's calculate disk capacity in binary, while hard disk makers advertise capacity in decimal. They're both describing the same number of bytes, they're just using a different method of measurement, sort of like using the metric and Imperial systems to measure the same distance. Even though the distance is the same, there will be fewer inches than centimeters. The only problem here is that binary and decimal use the same names to describe their different methods of measure.
Data transmissions (network, HD interface, memory speeds) are decimal because they are a measure per unit time which isn't binary. For example, current SCSI wide standards consist of a 2 byte transfer (16 bits) per clock doubled cycle (2 transfers per cycle). SCSI 320 runs at 80MHz (80 million cycles per second), so you multiply 80 million by 4 bytes (2 two byte transfers) and end up with the theoretical 320 milllion bytes/sec transfer rate (320MB/s). Notice because the clock rate is decimal (MHz = 1,000,000/sec, NOT 1,048,576/sec), that the final answer is a decimal value where MB - 1 million bytes, not 1,048,576 bytes.