Terminator 3 was much more expensive than HL2, but the market works differently for motion pictures. In most cases, the majority of the profits from movies come from when they make their run on cinemas across the world, the DVDs are usually just gravy for the studios. It's also worth noting that DVDs which approach the 30$ barrier are far and few between, simply because most people are not willing to pay that much for them. It's market economics at it's simplest: The seller wants to sell at the highest possible price, while the buyer wants to buy at the lowest possible price. At the end of the day, the seller will have to bow to the buyer's demands if he intends to sell anything, but that doesn't mean the seller has to sell at the lowest possible price, just at the level the buyer feels is reasonable.

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How do you know the world has gone mad?
It's when the world's best golfer is black, the world's best rapper is white, the French accuse the Americans of being snobbish, and Germany refuses to go to war.