I had an iMac and now have a Mac mini. The big advantage is that fixing and upgrading the latter is vastly easier. Apple could design an iMac that would easy to repair. It's designers are smart enough to do that. They could make opening the back easy and make it allow easy access to everything. But Apple doesn't bother. But the Mac mini is used in server farms and has to be repairable or it wouldn't sell.
The same is true of laptops. I can swap out the battery of my white MacBook in seconds and replace the hard drive and RAM in under ten minutes. Doing the same thing in the latest MacBook Airs is either impossible (RAM) or almost impossible (SSD). Replacing the battery is also a pain thanks to that glue. All Apple would have to do for the latter would be to replace that glue with Velcro.
Paradoxically, by making their products less repairable, Apple is making them less attractive to buy. Assuming, for instance, that my laptop will die in 2014, which would I want to own: a 2006 MacBook or a 2012 MBA. Obviously the former is better since it has long returned its purchase price. Stated in business terms, the harder a device is to repair, the faster it must return its purchase cost to make good business sense.