I believe that the OnChange event should fire when the up or down arrows are clicked.  Clicking the up and down arrow buttons is making a concrete decision to change the value of the textbox.  Similar to selecting a date in DatePicker fires OnChange, this should have the same expectation.

I have a numeric textbox that takes a large range and would never be changed sequentially.  For this reason, I would like to hide or disable the stepper control completely.  I think the most logical solution is to pass a null or empty value to the step parameter.  Can the control be updated to interpret the null such that the arrows are removed from the control?  I think this is a much better solution than modifying the appearance through CSS, and is less likely to be affected by subsequent control updates.