Capacity differences between iPhone and iPod Touch

Hi all. I'm feeling a little stumped here and could use some help.

First, I'd like to make sure that I'm computing capacity correctly. I know from reading the support article that there will be some differences between the capacity shown on our devices and what we calculate so that's not a problem. I'm calculating the expected capacity for my devices as follows:

iPhone (16 GB): 16,000,000,000/1,073,741,824 = 14.9 GB

iPod Touch (32 GB): 32,000,000,000/1,073,741,824 = 29.8 GB

As expected these amounts differ from the amounts listed on the devices themselves due to formatting, gremlins, etc. However, the following are the listed amounts as well as their percentages of the stated capacity:

iPhone: 11.9 GB (74.4%)

iPod Touch: 28.4 GB (88.8%)

Second, I'm wondering is if it is normal for the capacity percentage to be that much lower for the iPhone than it is for the iPod Touch. In the support article mentioned earlier it states that it's normal for a 32 GB device to show about 28 GB but is it normal for the 16 GB to show around 12 GB rather than around 14.2 GB which it would be using the same percentage of 88.8%? Thanks for any enlightenment about this.