If the 21.5" and 27" iMacs use the same i5 processor, why is it that the 21.5" can only be upgraded to 8G of RAM while the 27" can be upgraded to 16G? And why can you get the 1MB video card on the bigger unit?
Big_Al ... As far as I can tell, you can upgrade the 21.5 inch iMac to 16 GB of RAM, Apple just doesn't sell it that way. As for the video card, it is just how it is done. You gotta get this to get that. You can't get the SSD on the 21.5. I can't slam Apple on this, everyone plays these games. Dell is really awful. If you look at the specs for the iMac, you will notice both have 4 RAM slots, and use the same type of memory. Adding memory yourself on an iMac is WAY easy, BTW.
It might be down to the target audience. The people buying the lower model would be less inclined to go for the $1000 RAM upgrade as it's less likely they will need it. But you can upgrade it cheaper yourself:
The upgrades as mentioned above are just what Apple and other manufacturers do. In a way it makes sense because they can lower the costs on the low end and give people more reasons to buy the higher end models.