As someone who taught his grandmother to use a PC, I'm personally unconvinced that an iPad is a good option for older people.
The first issue is whether it is significantly less confusing than a PC. Sure, it is simpler (no multitasking), but when I was teaching my grandmother, multitasking was a 10% problem. She was mostly confused by the concept of hyperlinks, urls (when they weren't correctly formatted in emails, esp.), how to print, how to adjust font sizes, copy/paste, etc. The iPad certainly makes the concept of multiple windows easier to understand (by not allowing them), but there are still tons of issues with learning a computer.
On the negative side, it doesn't seem to be that good for an elderly person who may have some mobility issues. A desktop allows someone to position their head and hands in a reasonably comfortable way (head upright, hands below heart); I'm still not sure how the iPad is supposed to be used in a comfortable way. The iPad also has a significantly smaller screen and moving hands across the device might be a lot harder than using a mouse.