ipod has less than 30 gb of space

Just like a hard drive, you do not get the full 30gb of space. Some is lost due to the conversion. A byte is 1024 bits, etc, etc.

In addition, there is an operating system that is needed. All of that takes up some space. So 28.5 gb of space is pretty much exactly what to expect. Nothing wrong there.

As Joshua said, there is nothing wrong.
However, his explanation was a little incorrect.

Have a look here:
About iPod Hard Disk Size.

Some is lost due to the conversion. A byte is 1024 bits, etc, etc.
Just for clarification, there is nothing lost at all due to any conversion. The discrepancy exists merely because of a difference in the way a gigabyte is measured by hard drive manufacturers and how it is reported by the operating system.

Also, a byte is 8 bits, not 1024.

the 30GB comes with 28.5 actual capacity. but once i updated my iPod to my computer for the first time i was left with something around 27.8 GB

Right. The iPod firmware and software (games, extras, etc..) takes up a small amount of space as well.

8bits=1byte
1024 bytes=1kb
1024kb=1mb
1024mb=1gb....turns out 30gb isn't really 30,000,000,000 bytes and your iPod doesn't really hold 30gb in a practical sense