In a way, both Crucial and Apple are correct.
Let me explain:
You see, the Apple iMac last saw a refresh over a year ago, in May 2011and at the time 16gB was the maximum memory supported for the Apple iMac due to the fact that only 4GB memory modules in a 1333Mhz configuration were available and even a year ago it would cost you over $100 for 8GB of RAM for the iMac and a whopping $400 if you bought the RAM from Apple directly.
So, when Apple released the iMac they stated that 16GB was the maximum ram you can buy by upgrading all four available memory slots with 4GB DDR 3 SDRAM sodimms: 4x4GB = 16GB
Fast forward to today where you can buy 8GB memory modules for iMac that were not available at the time of the iMac’s release date, so in this case Crucial is correct because if you were to buy 4x8GB DDR3 sodimms for the iMac from Crucial you’d have 32GB installed.
Is It Safe To Install 32GB of RAM into an Apple iMac
Here’s the tricky part. It’s more than likely OK that you’ll be fine installing 32GB of RAM in your iMac and seeing that the recommendation comes from Crucial and not some questionable seller on eBay I’m going to stick my neck out and say you’ll probably be fine with the 32GB in your iMac. After all, Crucial’s big slogan is that crucial memory is guaranteed to work with your computer.
All this said, because Apple states the maximum of 16GB, that’s where I would stop. Why? Because there’s a good chance your warranty is toast if you install more than the amount of RAM recommended by Apple at the time of release.
I know that personally, with my Mac Mini bought in March, I stopped at 8Gb even though I could technically install 16GB in my Mac Mini I choose not to because I didn’t want to void my one year of Applecare and adding more ram than what Apple suggests could do that. Perhaps when I replace the Mac Mini or the Applecare Warranty lapses I may attempt an upgrade of more RAM.
It all comes down to how comfortable you are with voiding your warranty in the rare case that something may go wrong with 32GB of RAM in a 2011 iMac.
I can’t recommend you go higher than 16GB of RAM, regardless of memory upgrade advice from Crucial.