The upsell. People who don’t need 16GB will not care. People who do will pay it. That’s basically free money.

Reverse future proofing. If you think 8GB is cramped now, imagine 3-4 years from now when most of these computers will still be in use. Users may hit the upgrade cycle quicker.

Profit margins. After the return of Steve Jobs, Apple simple will not sell any hardware without a hefty profit margin.