I imagine Thor is more likely...Is your friends name Wulfgar??
Recently in my games I've instituted a houserule that Throwing is no longer a enhancement bonus cost to add to a weapon but is instead a straight +2000gp price to get the same effect.
Thoughts?
I think it'd be better to make returning the flat cost and leave throwing as a +1 property. Non-throwing weapons are plainly superior to ones with a listed increment, and by making the addition of the throwing property only 2000 gp with no "rising cost" due to future enhancements, you're basically just making actual throwing weapons obsolete after the first 5 levels or so. Compare trident with longsword. Would you be ok with a trident user getting the Keen property for a flat 2000 gp?
Throwing and returning are great weapon enhancements to have for a class like the Dwarven Defenders who have movement restrictions when in a defensive stance. Beyond that I've found them not worth the effort or money.