I use the cursor keys on the numpad all the time. 99.999% of the time it's in the cursor key mode and I hate it when I accidentally hit the numlock key and it comes out of it, or when someone else uses my keyboard and purposely toggles it. If I use a keyboard with the separate cursor keys, I still always use the ones in the numpad. I began with computers back before PC even existed, and when IBM came out with the PC then XT, and later AT, I had each of those models and the use of the cursor keys in the numpad became second nature. I find it extremely clumsy to use the new-fangled dedicated cursor cluster introduced on the Model M. Which is why the IBM PC AT keyboard is my all-time favorite.
Many people actually don't use the cursor keys all that much. If they're just composing text, they typically type from beginning to end and probably only use the backspace key. If they need to jump around, chances are probably good they'll use a mouse. A lot of my time spent on the keyboard is for coding though, and moving the cursor around is an integral part of that (up line, down line, beginning of line, end of line, etc.). Cursor keys end up being a significant percent of my total keystrokes. The numpad cursor keys are laid out perfectly for this purpose. With left/right/up/down in a +, not and inverted T configuration, and Home, End, Page Up, Page Down being very logically positioned in the cluster. And it's just a 3x3 matrix which is super easy to use. Way better then the standard cursor cluster which is in the area of a 3x5 matrix, requiring much more finger movement (more time required to hit the keys), and more chance of error.