What is your rational behind "changing" it up? Because u read that in Flex/bb.com and its "the thing" to do? So if the pump doesnt mean u are growing more, what does feeling nothing at all from heavy curls mean?
Change it up because maybe he's bored with the routine and not putting much effort into it.
Do you do the same exercises/reps every workout, every week, every month, every year

I missed it, where does he say he doesn't feel anything at all from going heavy? I like to go heavy for a couple of weeks, go light for a couple of weeks, use supersets a few weeks, giant sets a few weeks......light, heavy, medium, it's all good.