Although I don't like the carving up of content for sale as DLC.....
I don't agree that we're getting less game. And this coming from a guy who obsessively treads down Nostalgia lane, playing stuff like Dragon Warrior 1 - 4, Dragon Quest and Final Fantasies on like a yearly basis.
I'll keep going with your pie analogy that comic posed.
Commence epic pie analogy.
In the late 80s and 90s, games were Apple Pies. They were delicious, novel and we were reasonably satisfied because we'd had very little quality pie up to that point, and suddenly everyone was making Apple Pie and doing it pretty well.
As time went on, Apple Pie just didn't cut it. But that's ok, because now developers were making Pecan Pie, Blueberry Pie and some shit that doesn't even resemble pie, like cake.
Continuing further on, in the last 90s, we now had dozens of kinds of pies for every person out there and so in an effort to keep satisfying our rising expectations of pie, developers started putting more things on the pie. Some of them were just nice to look at, and a lot of time was spent just doing that. All sorts of things were put on top of it though, like whip cream, drizzles of extra flavor, double fillings, even an obligatory thick crust just for those people who said they want their pie to take a while to eat.
After a while, developers realized they couldn't keep this up indefinitely. Our expectations of a better pie every year outstripped their ability to think up new kinds of pies, new ways to make that same pie more interesting or how to cram more in the pie while still making it bake-able and appetizing.
So they made a choice. Maybe all people don't want that stuff on their pie. And maybe the people that DO are willing to pay a little extra for it. They still put some whip cream on your pie and you can still get hundreds of different kinds of pie, but if you don't need to you don't pay extra. You're still getting a delicious pie at the peak of pie-development technology.
When you do pay extra, you're paying for your two scoops of ice cream, chocolate chips, sliced fruit on the side and an extra ramakin of something sweet just in case you haven't already slipped into a sublime diabetic coma.
End Epic Pie analogy.
So I agree with Tridus on this and the data backs him up. People generally DON'T finish epically long SP games (I'd never really thought of the usefulness of achievements as a tracking method.) And those that do DON'T necessarily go out and buy more content because they haven't gotten their fill. Even IF, for example, I'd had access to all the Resident Evil 5 DLC at release, there's no guarantee I would have played it. (I would have.) I never finished it SP. It took coop for me to care enough about the game itself to finish. And while I want more Mercenaries content, I _didn't_ want it bad enough to pay for it.
So on one hand, we have everyone asking for the game they want developers to make. And on the other, we have developers and publishers who have over-committed to stuff and been left high and dry by most gamers. The most reasonable way for them to provide all things to all people: games with a lot of content and jobs to the people that make the content, in some sense they're rightly putting the responsibility for that content on the purchaser.
Because let's not be total snobs here. In my lifetime games have evolved significantly from the A Button B Button days. These are technological marvels that we get to play with everyday and that most people can afford. Resident Evil 5, Devil May Cry, Dungeons, The Witchers, Mass Effects, Dragon Ages, Neverwinter Nights, Assassin's Creeds Starcraft II and even Diablo III... these are solid games with a lot of content that makes NES RPGs seem simplistic. (So simplistic in fact that numerous indie games are now making money on exactly that format, because people our age that grew up with them are now making them.)
They simply can't match our expectations as gamers or our capacity for imagining a better game. We're not satisfied with good enough for what we pay and maybe we shouldn't be. But if we're even giving an iota of credit where it's due, the games are not at fault and publishers aren't completely fucking over everyone with things like DLC. It is in fact possibly the most rational business choice they can make when they're at the head of a billion dollar industry and satisfying modern gamer's expectations is a multi-million dollar hit or miss on every title.