RRilef said:
First off I have to say if you don't have the OB I would highly recommend it, its only 10 dollars for five of the highest rated games of all time.
Secondly, how and why do you think valve does it? This price is so ridiculously low, if I bought a game off of ebay, I'd pay half of it just for shipping, not to mention I'm getting five games.
Edit: This is off of steam for those of you who don't know, http://store.steampowered.com/sub/469/
Edit2: What happens when you play HL 2 HL 2:1 and HL 2:2? You're going to want to play HL 2:3. Combine that with http://whatsinthebox.nl/ and there is the perfect storm. I can only hope
The short answer, valve does it because they can afford to. The long answer.
Valve has already made huge profits off of orange box. The cost of developing the game is long past paid for. They could literally price the game at just about any price now and make a profit of it (via digital distribution anyway). Valve has sales on games for 2 reasons. The first of which, as is the case with orange box, is to stimulate sales and generate an immense profit off of a game that's already paid for its development cost several times over. Being that orange box has been out for 2 years now, sales have dropped off and they are no longer making very much money off of it. As stated earlier, that's ok because they've already made buttloads of money on the project. However, dropping the price in order to stimulate sales generates a huge revenue for them over one weekend. For instance, in any given weekend they might sell 1,000 copies of orange box (purely speculative figure) for 20$ or however much it sells for. In one weekend, they drop the price to 10$ and they sell 10,000 copies, thus generating 5 times the profit for that game on one weekend than they would any other weekend.
The second reason for a drop in sale price (and really is the same reason) is to stimulate sales on a product that wasn't selling to expectations. Dropping the sale price once again stimulates people to buy it. As you can imagine, there's generally a huge overhead on software. What they weren't making by selling the product at a higher price, they hope to make up for by dropping the price and selling in quantity. (UT3 for example).
Anyway, I hope this answers your question. It's not because Valve is an amazingly generous company, it's because Valve has an excellent business model. They're not taking a loss on anything, everything they do makes good business sense.