iFixit likes to take stuff apart to see what they are made of and in the same time check how easy it is to repair the product. When they did that to the Retina MacBook Pro it got a low repairability score and the iPhone 4 / 4S didn’t get that high up on the scale.
In the recent iPhone 5 Teardown they give some kudos to Apple for making the Display Assembly easy to replace. This is probably the part people need to exchange the most so it welcome that it is easy to change. The disassembly also shows us the new A6 processor and the battery.
Head over to iFixit if you want to see more on how the iPhone 5 looks like inside.