What about the costs of development and the costs of designing / buying / implementing the advanced tooling that shimano would use?
If you can't see the improvements in the new brake then you probably haven't tried them both - the old lever had a number of flaws that are now fixed, and a number of changes have been made to allow the brake to be lighter (from what I can see - eg. lever, 2 bolts instead of 4 bolts clamping caliper, aluminium hose hardware) and better at cooling.
For what it's worth I don't currently own any Shimano brakes (I run Formula) but I think they develop some very good products and the prices aren't unreasonable when you take that into account. They also aren't the marketing machine you suggest IMO - a lot of people that buy their products just seem to be happy repeat customers.