Because... ?
Please, lets not leave accusations baseless.
All the sentences after that were the 'base'.
The cost for all this is the same regardless of the device's memory capacity. It doesn't excuse such a huge markup for an upgrade that costs them so little.
So lets say company A makes a product that they want to sell for $100. It costs them $50 to make. They used $10,000 in R&D. They only end up selling 100 of them over the course of the first year. That means they made negative $5000 the first year. (I'm not including dozens of other costs) The numbers are obviously way off in Apple's case, but basically yes, it does allow a huge markup.
I run a business myself where the markup seems 'huge', but after accounting taxes, operating costs, shipping cost, credit card fees, employee wages, rent, electrical bill, water, shipping supplies, business assets and returns, it gets drastically cut down.
Because the other companies have SD/MicroSD expansion slots? So you have the choice of buying their expensive memory upgrade or buying one yourself in a less expensive form or at a later time when memory prices have fallen? Whereas with an iDevice whatever capacity you buy you're stuck with for the life of the device, so if you find down the line you need more space from a growing app collection or iTunes media library you're SOL unless you buy a whole new device, when an owner of other products can buy a much cheaper expansion card?
This is a whole other debate, that I'd rather avoid.
You tell me.