There are no good or bad ideas :) Its all about time, place, knowledge of tradeoffs, execution, business, marketing, taking into account all stakeholders (user is one of them) and everything holistic :)
What you say is true, a finger is not a mouse. But we're now a decade past the release of iPhone, and by this time, the industry in general (and Apple in particular) have deep knowledge about all the tradeoffs involved here. 5 years before and this can be considered a reckless bet that requires a Steve Jobs to pull out. Now, its just natural evolution. Responsive design has been around for even longer, and changing interactions based on screen and form factors is a pretty mature problem domain now.
To be very specific:
- whether its a finger or mouse can be a runtime decision, not necessarily a compile-time or clean-slate/distribution decision for different platforms
- those decisions are already standardized enough based on existing knowledge that you can let the platform/framework (or 3p libraries) handle it out-of-the-box for you and just register multiple possibilities. instead of debating finger vs mouse - think finger and mouse
i.e. different interactions requiring entirely different apps - is not necessarily true for all of them. for a 2D application, some amount of standardization is actually good, otherwise it doesn't really help all the interaction patterns and may instead stagnate them.
Is my anecdotal too far off?
If you look at the PPC->Intel timeline[1], Apple announced it 6 months in advance, although it went fairly quickly after that.
1: https://en.wikipedia.org/wiki/Apple%27s_transition_to_Intel_...
Thankfully Apple comprises vastly smarter people than me, but I've always thought this is a bad idea.
The two interaction models are so dramatically different that I don't see how merging them makes sense. A finger is not a mouse.