Numbers' main competitor is Microsoft Excel. At its introductory demonstration, Steve Jobs pitched a more usable interface understandable to lay-people and offering better control over the appearance and presentation of tables of data.
A "Layout of Lists" metaphor, where spreadsheets are arranged on a canvas and can be positioned and sized independently there along with charts and graphics. This can make different tables on the same sheet easier to style and delineate to users. It also eases presentation-centric work.
Highly table-centric workflow, where lists are easy to structure with headers and summaries.
Checkbox, slider, and pulldown list cells.
Drag and drop of functions from a sidebar into cells.
A Print Preview that allows all editing functions while previewing, as well as realtime scaling and moving of tables to arrange them freely on the page(s).
An XML native file format, using document bundles to contain media and associated files.