According to the release notes, the iMac SMC Firmware Update 1.1 is recommended for iMacs equipped with flash-only storage, otherwise known as solid state drives.
This update improves the Power Nap feature in Mavericks on your flash based iMac by allowing it to perform silently, without spinning up the fan.
Power Nap periodically updates apps, such as Mail, Contacts, and Calendar, and will download software updates while your iMac is sleeping.
The update comes in at 921KB and can be downloaded through Apple's Support Downloads webpage or Software Update.
Apple's iMac 10.8.5 Supplemental Update 1.0 again pertains to late-2013, but is limited to those machines configured with NVIDIA GeForce GT 750M graphics cards running OS X Mountain Lion 10.8.5.
The update fixes an issue that may cause external hard drives to be ejected when the computer goes to sleep, as well as a problem that would prevent USB Bluetooth adapters from working.
The Supplemental Update weighs in at 17.11MB and can be downloaded via Apple's website or Software Update.