The NPD have released their figures for US PC retail sales in 2007, as reported by GameDaily. The biggest sellers? I'm glad you asked.
1. World of Warcraft: Burning Crusade – Vivendi (Blizzard) – 2.25 million
2. World of Warcraft – Vivendi (Blizzard) – 914K
3. The Sims 2 – Electronic Arts – 534K
4. The Sims 2 Seasons Expansion Pack – Electronic Arts – 433K
5. Call of Duty 4: Modern Warfare – Activision – 383K
6. Command & Conquer 3: Tiberium Wars – Electronic Arts – 350K
7. MS Age of Empires III – Microsoft – 313K
8. Sim City 4 - Electronic Arts – 294K
9. MS Flight Simulator X - Microsoft - 280K
10. The Sims 2 Bon Voyage Expansion Pack – Electronic Arts – 272K
That includes sales from every multi-pack you can imagine. The total value of PC Games retail is $910 million, which is down $60 million from 2006 (Which itself was up from 2005's $953 million (Which was down from 2004's $1.1 Billion (No, really))).
And some analysis follows. Maybe even with jokes added to taste.
There's two main ways you can look at these figures. There's the obvious way, and the apologist way. The obvious way - as the name suggests - takes the obvious route of noting that PC sales are beneath a billion dollars and falling, enormously dwarfed by console sales, the only things selling are sequels and we should all pack up and go home. The apologist way makes excuses.
Problem being, the apologist in this case is completely right. As the NPD's own analysts note, the PC market is simply in a different place to the console ones, and the sales the NPD charts are a relatively small snapshot of the market. It doesn't include any Digital Downloads, whether from large portals like STEAM or direct from individual companies. It doesn't include any of the casual market. It doesn't include an MMO monthly fee of any kind, whether a World-of-Warcraft-like traditional monthly fee or micropayments.
(Hell - you want to drag in stuff like educational games, art games, advert funded stuff, military commissions (Flashpoint's VBS1, for example) or any of that sort of oblique stuff where people are earning money from non retail sources. Which only happen on home computers...)
(Oh - and it's also only the American figures. America isn't the world and all market-places aren't the same. While a smaller market, have a look at the multiformat charts from Sweden which turned up in the Quarter To Three thread on this very topic.)
(It's worth stressing that the NPD figures do include online retailers like Amazon.)
In other words, the PC is a complicated place and retail can - to brutally paraphrase the Costikyan position - probably go and fuck itself. PC games have always had trouble with the buy/trade/second-hand model which most bricks-and-mortar shops concentrate on - i.e. Shops make a far larger margin on re-selling stuff than selling new games, so concentrate on it, to the point where it's actually hard to talk a shop into selling you a new copy of a game when they have a resale one sitting on the shelves. PC don't have the second-hand market, therefore leads to less profit, so is less concentrated on, so... well, you get the picture. Of course, the PC being the major gaming format where developers and publishers can do whatever they want to has lead to all the alternate revenue sources detailed above.
The big unanswered question is exactly how much money does come from these channels. You'll note there's no sign of the Orange Box in the Top 10 - and that's a major game which rests heavily on the new download model. Until Valve choose to release some manner of figures for that and other games on STEAM, the actual true picture of the health of the PC games industry will be shrouded in guesswork, theory and hotly-argued comments threads like the one below.