Apparently the example page on http://trirand.com/blog/jqgrid/jqgrid.html is wrong; I figuredout how to get to the actual page source of the example and saw the additional option of:

multiboxonly:true,

Which got the desired behavior. You may want to update your example to be correct.

As long as I'm posting again, I really do want to say thank you for a great piece of software.