The navigation system in my car has a 20GB hard drive, runs Linux, and arguably has more power than an iPhone. I'm still not regretting the fact that I can't load software on it. When I'm trying to get somewhere, I just want the GPS to work - I really don't want to see it crash because I loaded a dodgy piece of crapware on it.

Likewise, the first time a customer tries to make a phone call and instead gets a pop up ad saying "YOUR PHONE IS AT RISK!!!!1!!!11!1!" you will know you failed at delivering a successful smartphone experience.