Ahhh. You caught me. Regarding this, I feel this is all personal preferences.
While I do not like many extra app icons on my enlarged phone, I certainly do not want my iPhone to maintain the same number of apps on the home screen, only that the app icons are spaced out and enlarged.
When you do this, it affects alot of things.
These theories are certainly made up in my mind to counter your comment
1. Distinction
If you simply spaced out the app icons more, people can't distinct. This is actually a sales marketing thing. Its like ''My new iPhone 5 has a bigger screen, yet people can't distinct it enough because it still has the same number of app icons.'' compared to ''My new iPhone 5 has a bigger screen, at least people can distinct it with alot of app icons.''
Of course, this factor seems abit redundant even to myself, but still... it will happen.
2. Aesthetics
While adding more and more app icons is not weird but is still tad confusing, retaining the number of app icons is another thing. When you have the extra screen size, it is only a natural thing to add more content, not decrease the content.
The iPad is another thing. Its a tablet. Content is much more far away as you would usually use the iPad at a distance away from you. This means you can't clutter the home screen as users will find it abit hard to differentiate and maybe find it confusing. Try placing the iPad at the normal distance away from you and imagine it cluttered with icons.
For the iPhone, it is still possible to clutter the home screen, with my render posted above. However again, cluttering the home screen is still not right as it is still confusing nevertheless, but not as bad as the one on the iPad.