When I use insertRow it returns an error that I can't shift cells of a worksheet. It seems the number of rows is at max the number of received rows, or 200.
I attached a screenshot showing that manually executing the commands does not work, but neither do the buttons for the user to insert a new row.
I changed your dojo example to show the problem: http://dojo.telerik.com/aguKo
As you can see all rows are filled. If I wanted to add a new row I'd press the 'Insert Row' or go to the 'Insert' tab and press the button there, but I receive an error right after it.