A 70% take would have blown the minds of developers pre-Steam. Retailers took 40% and were ruthless about shelf space and inventory. Distributors took 20%. Plus you had to actually make a box/CD/etc. They were lucky to keep 30% not pay it.

This doesn't mean Valve is perfect but if a developer is "suffering" because of a 30% cut they probably need to improve their pricing/game/community/etc.