I think I understand your argument now. Why do you think browsers as de factor operating systems is wrong? Their programming interface is highly standardized across implementations.
> Their programming interface is highly standardized across implementations.
It may be easier to have everyone use the same software and hardware platform everywhere. After all we do want interoperability and we do want everyone to play well with others, but, standardization and portability is a push to stop people from trying new things. The push to standardize everything is an unfortunate consequence of not having a separation of concerns, separate concerns such as content and UI.
A smaller contact area between implementations means we need only be concerned about compatibility at that interface and the rest is up to you. This keeps the area of software that we can't change to a minimum.
