These are two completely independent factors.
There is nothing magical about a touch screen that instantly removes all the complexity in an operating system: you're drawing false correlations. "This tablet X is easier to install applications on than this computer Y. Therefore, touch interfaces make installing applications easier."
My mom is paranoid about viruses and installed Symantec, but the paranoia also ensures that they don't click on weird crap coming thru email. Sidenote: my mom upgraded the laptop herself from Vista to Win7 without bugging me, praise jeebus!
PCs aren't mystical, I don't know if the expertise of maintaining them is some kind of totem that geeks cling to but hearing about problems with them is the exception instead of the rule these days.
There are other tasks like managing photos, watching and editing movies, installing third-party software, and more that I bet your parents have trouble with or flat-out avoid on a PC. These things are easy on an iPad. Not to mention the constant threat of malware, no matter how paranoid your mom is.
If there's a totem that geeks cling to, it's the fear of the PC going away and the fantasy that PCs aren't overly complicated to an embarrassing degree, or that everyone can magically learn how to use PCs if they'd just spend hours every night on them like geeks do. It's symptomatic of a real lack of perspective when it comes to how the public deals with the standard PC. You and I think they're easy because we spend most of our time on them. They are our living or our hobby. Most people aren't like that.
Additionally, you generally don't need to know how to update yur drivers or antivirus. Those get updated automatically on Windows. The only thing you need to know how to do is install applications. Which 95% of the time is to double-click setup.exe or install.exe.
I'm the tech support guy for my extended family. I support around 30 or so computers. What I've found interesting is over the past year or two is that support calls have dropped to about one every other month. And they're no longer things like, "My computer isn't working." They're more like, "How do I know that the backup program will work when I need it?"
On a tablet, there is no running an installer executable. You just tap. Uninstallation is also just a tap. It's undeniably superior.