You're right that taking three tap for paste away is a use case change, but it's not as big of a change as moving one response from one action to a different action.
Another thing to note is that Ubuntu tries to cater to people who come from all environments. The X copy/paste functionality is sort of an oddity in desktop systems. It ends up confusing people who aren't used to it. An argument could be made that although it can be used effectively, making it less easy to use would not be very harmful to the majority of users. All these aspects have been weighed against the ability to add meaningful gesture use cases, and the design team at Canonical believes this is the best approach at this time.
Ian,
You're right that taking three tap for paste away is a use case change, but it's not as big of a change as moving one response from one action to a different action.
Another thing to note is that Ubuntu tries to cater to people who come from all environments. The X copy/paste functionality is sort of an oddity in desktop systems. It ends up confusing people who aren't used to it. An argument could be made that although it can be used effectively, making it less easy to use would not be very harmful to the majority of users. All these aspects have been weighed against the ability to add meaningful gesture use cases, and the design team at Canonical believes this is the best approach at this time.