in excel it is easy to add the same number to non-adjacent cells. How does one do it in Calc?
An implementation of the feature should be a rather easy hack for a developer. Therefore I assume it was a conscious decision not to do it. It may be error-prone in use and actually wanted by very few users.
Anyway, it isn’t exactly difficult to write a bit of Basic code performing the task in a similar way as it is done for single cell ranges using Alt+Enter.
In pursuit of the other question I linked to above I did a “proof of concept”. The code is contained in this attached demo.