iMac Memory Upgrade

I bumped our iMac memory from 4 gig to 12 gig, I added two 4 gig chip sets.  I ordered Samsung memory because that is what Apple uses.  Ordered it through Amazon on Sunday, arrived today from California and installed in less than 10 minutes.  I priced the memory through Apple; they wanted $200.  The price I paid through Amazon including shipping was $65.48.  Why did I bump the memory?  Apple came out two weeks ago with a new operating system called Mountain Lion (we have Lion). My research told me it is a memory hog, so before I upgrade I felt I needed to beef up the computer.  By the way I could have bought cheaper memory, but I decided to keep it  OEM.