One thing to note is that hardware and OSs exist to run apps. Some of these apps are built-in like Phone or Mail.
However, most are not, and may never exist outside that OS - games are a good example. When will Skype and Webex (two very important work uses of my phone) come to FFOS?
These problems go away if you are not courting heavy app users, but I would not call this an "App Silo" - these are investments people have made in time, knowledge and perhaps money, and even if they exist on another OS (see reviews for various Android apps that migrated from iOS like Audible) may not ever have the same feature set or usability.
That does not make the transition from iOS to Android or vice versa easier. Once you have invested in one ecosystem, you lose your investment if you switch.
That does not happen on the web, where you can switch from a browser to another with a very marginal cost.
