In October 2012 Android added the ability to support multiple user accounts in version 4.2 (Jelly Bean) so that multiple users can customize their tablet experience, from lockscreen to wallpaper, apps and folders. It's just common sense that two people sharing a tablet would want to see their own accounts when they look at email and calendars.
Android 4.3 (announced July 24) takes it up a notch with "Restricted profiles for tablets" which can be used to limit access for children (like iOS' Parental Controls feature), but it can also be used for POS terminals and kiosks in retail stores.
Sadly, multiple user support doesn't appear to be coming in iOS 7, so it could easily be another year (or more) before we see the feature on the iPad. What a shame.
I hate to be a conspiracy theorist but there's only one reason why Apple would deprioritize such a needed feature: it doesn't want family members sharing an iPad because Apple wants you to buy separate iPads for everyone in your household.
Is this Apple's idea of "multiple accounts?"
Update: According to TechCrunch the multiple user accounts feature is only on Android tablets because Nokia patented it for phones.