Perhaps, but for the majority of users, the iOS security model happens to be extraordinarily effective. I'm not saying Microsoft should force this down everyone's throats, but I for one wouldn't see it as a bad thing if something along these lines was the default on retail purchased PCs.
I say this as the "free" family tech support officer.
I've moved about half of my extended family onto iPads and my life is much better.
I understand where you're coming from but it's a little like saying that North Korea enjoys a low crime rate.
Do we want one company to have that much control? How do you think personal computing would have evolved if Microsoft had controlled Windows applications the way that Apple controls iOS applications?
One of the best things that ever happened was Windows and the web both flourishing as massive market share, mostly-open development platforms for almost two decades.
I don't disagree, but let's not blur the lines here between people who use computers professionally and people who use computers as an appliance.
We could have had an iOS-like security model on Windows for the majority of unassuming retail customers and I don't think it would have made a single jot of difference to wider flourishing.
(In fact, for various reasons, I would wager that we'd have a more mature technology sector. Don't underestimate the damage caused by malware to consumer trust.)
Web development as we know it would not exist. Microsoft would have banned competing browser engines (as is the case on iOS) and IE6 would have had 90% market share. The preferred way of doing active content would be ActiveX.
That's still a huge majority of PCs. The self-built PC has always been a bit of a market anomaly; people don't have self-built Macs and self-built cars are a truly tiny number.
And I'm working on the assumption that this would have applied decades ago, when there weren't quite so many viable alternatives to the PC and Microsoft was the terrifying market monopolist.
The difference is that it's voluntary. Apple has competitors. If they are too strict with their policies, developers will get angry, customers will get angry and eventually both will switch to a competitor.
Apple has a strong interest in finding the right compromise between control, convenience and diversity.
I say this as the "free" family tech support officer.
I've moved about half of my extended family onto iPads and my life is much better.