Why does Ubuntu show 1GB more storage space than Android has?

Why does Ubuntu 13.10 show 1GB more free space than Android 4.4.2?

Linux:

Looking at the new 16GB/12.5GB Nexus 5 which T-Mobile sent me to replace the almost useless 4GB/600MB LG Optimus F3:

I'm now done installing necessary apps into the internal memory:

It seems, after the Android OS was installed, there was roughly

The pre-installed apps took up another few hundred MB such that the 16GB Android 4.4.2 phone started with about 12.28GB:

Then, after I installed a dozen or so basic smartphone apps:

The phone was left with about 10.72GB of available space:

Note: There is absolutely no user "data" yet; we're just talking about pre-installed and post-installed basic apps.

So, just "my" list of basic apps alone, seem to take up (roughly) about 2GB of storage space (this includes offline road maps for California, which are a necessity, IMHO, for when you really need it when there is no cell signal or your data plan is low).

However, when I plug in that 12.5GB Nexus 5 into Linux, Ubuntu Saucy Salamander shows "free space" of about 11.5GB, which is actually 1GB too high as compared to what Android