With the new retina displays on laptops (and coming soon to desktops) you'll notice the difference in MPs
zoom in 100% on an iphone 5 picture and you'll notice it isn't perfectly sharp whatever display you're using. these lenses are optically incapable of resolving a full 8 megapixels most of the time, just as 16 megapixels is a waste on a $200 compact.
apple is making the right move here, i just wish it went a little further. sony's z1 has a straight-up point-and-shoot sensor inside it with little form factor compromise, but it's like 20 megapixels for no good reason. make a sensor of that size 8 megapixels with an f/2.0 lens and you'd have pretty much the perfect phone camera.
still, no-one seems to get image processing and software as well as apple does. unless rivals have upped their game in that department, i expect the 5s to take better pictures than pretty much any sane phone in most situations.