That is true, but in my experience third-party SSDs don't include the reserve space in the advertised drive size. For example, I have several "60GB" drives tha

That is true, but in my experience third-party SSDs don't include the reserve space in the advertised drive size. For example, I have several "60GB" drives that actually have 64GB of internal storage but the extra 4GB is reserved. I also have several "128GB" drive that actually do show up as 128GB to the OS, meaning the reserve space is in addition to the 128GB, not part of it. Another 120GB drive I has reports the exact same binary size (112GiB) as the Macbook Air "128GB". So it appears that Apple is including the reserve space in the advertised drive size while third-party SSDs do not.