I am slightly concerned that you might have got mixed up different concepts here. One is simplistic design which users with little or no previous experience can still feel comfortable to use on their own. A second is enforced uniformed interface cross multiple application which users feel familiar with (and thus also comfortable with). The third is safety against malware, which is a security concern. The last is market and user incentives.
A device without a walled garden can still maintain a simplistic design, encourage a uniformed interface, and maintain a similar security against malware. However, it has a harder time to incentivize software developers to strictly follow the uniformed interface and to always use the official store. Android market place has also less incentives to turn away new software, because developers has an alternative (thus Android app store have incentives to be lenient). For the Iphone app store, there are no alternatives for developers so Apple can be as harsh they want (thus they have incentives to be harsh).
Unwalled gardens also has a harder time to discourage users to run unknown software with malware in them. In practice, iphone users are less likely to try run downloaded software from a random internet site (or dl via bittorent), because no legit iphone developer ask them to do it. Android developers however often teaches users to use third-party stores. Thus, a android virus has a much easier time spreading than a Iphone one because on user base are trained to run untrustworthy programs, and one user base is not.
Thus a walled garden has two functions. First it maintain a monopoly grasp on a market, to extract tax on each purchase. Second, it provide incentives to developers so they follow a strict uniformed interface, to App store approvers so they will be more strict in judging new software, and to users so they are less inclined to run untrusthworthy software.
The first thing should be regulated away. The second thing should be understood when designing unwalled devices so to create the correct incentive for everyone.
A device without a walled garden can still maintain a simplistic design, encourage a uniformed interface, and maintain a similar security against malware. However, it has a harder time to incentivize software developers to strictly follow the uniformed interface and to always use the official store. Android market place has also less incentives to turn away new software, because developers has an alternative (thus Android app store have incentives to be lenient). For the Iphone app store, there are no alternatives for developers so Apple can be as harsh they want (thus they have incentives to be harsh).
Unwalled gardens also has a harder time to discourage users to run unknown software with malware in them. In practice, iphone users are less likely to try run downloaded software from a random internet site (or dl via bittorent), because no legit iphone developer ask them to do it. Android developers however often teaches users to use third-party stores. Thus, a android virus has a much easier time spreading than a Iphone one because on user base are trained to run untrustworthy programs, and one user base is not.
Thus a walled garden has two functions. First it maintain a monopoly grasp on a market, to extract tax on each purchase. Second, it provide incentives to developers so they follow a strict uniformed interface, to App store approvers so they will be more strict in judging new software, and to users so they are less inclined to run untrusthworthy software.
The first thing should be regulated away. The second thing should be understood when designing unwalled devices so to create the correct incentive for everyone.