I think these days, there are games that are marketed for online and offline play. I think that by now most gamers will know that games like "Call of Duty" or "Left 4 Dead" is an online experience with a campaign experience that's minor in varying degrees to the centerpiece, which is the online. Certain systems are more prone to the online experience because that's what they system itself is built to do. Even games like Fallout work fine offline, but to get the full experience of them (patches, DLC), you have to be online to play them.
I think in this day and age, unless you're cranking out a game like Fallout which is potentially 100+ hours long, you've got to have some sort of online component or your game is going to lose out to those games that go online. And why not? Nobody wants to pay for online service to get games that don't use it. For example, look at games with the non-multiplayer component... "Dante's Inferno," "Bayonetta," "Batman: AA," "Dead Space," even to an extent "God of War 3," all of them had no online component, all of them saw strong initial sales, but then price drops 60-90 days after their release, all of them saw their resale fall through the floor... Dante's Inferno is, what... Less than a year old? I can go down to BJ's and buy a copy for $11. Dante tried to cut off the bleeding by adding a co-op later, but by then cuts had already hit. And games, like "Bioshock 2" and "Medal of Honor" suffered hard from bad multiplayer experiences, while "Battlefield Bad Company 2" shot up from minor release to a huge word-of-mouth game that actually had a price drop reversed after buzz drove people to buy it. Now we're starting to see games get dinged by reviewers and players for lack of multiplayer or co-op... Like "Fable 3" or even "New Vegas."
For gaming companies, the online is the money maker... It's what keeps the game new and fresh and keeps people playing. "Modern Warfare 2" is how old and still almost full priced and an insanely expensive purchase used? Halo? Now we see games like "Bioshock 3" bragging about revamped online, the beta multiplayer on the sequel to "Dead Space" has gotten amazing buzz, the new AC seems to have legs thanks to a new online component, "Red Dead Redeption" is another one that is surviving quite well due to the online, and even "Borderlands" is the same way... Rejuvinated in sales by great online experiences.
And honestly, most people don't say "If I'm going to spend $60, this had better be a good single player game..." They say "If I'm going to spend $60 on this, it'd better have a lot to do..." and I won't lie, I put down "Alan Wake" for "Red Dead" even though, IMHO, "Alan Wake" was the better game, because "Red Dead" seemed like with the campaign and the online, it was a better use of my $60 simply because it seems like it'd do more to hold my interest for longer. For that kind of money, I expect it'll do more and be more than a single player game. If that's the kind of experience I want, I will cancel my gold (or platinum or whatever it is) XBL account and take up the Wii.
And I do so get tired of hearing complaints about the offline aspect of games like Halo, CoD, L4D, etc... These are games that are marketed very specifically for online play in almost every way. So complaining that has little to offer in terms of offline or single player play is on par, for me, with hearing that "Plants vs. Zombies" was a poor excuse for a first person shooter. In both cases, the answer is "Well of course it is, that wasn't what the game was supposed to be."
Honestly, what I wish beyond wishes was that Microsoft would stop with this stupid trend of requiring you to be online when you play DLC or downloaded games you buy off the Marketplace. Do you know how frustrating it is to have a game like Fallout 3 in with all the DLC you paid for and loaded on, but having the DLC unavailable unless you're online and playing? It's not like you're even online playing with other people, you're just online. It's insane. Why should I have to connect to XBL to play PvZ or Bioshock DLC? AAARGH!!!!
Though I do sympathize with the online stupidity of the general public. I get a lot of it on some games (Gears of War, Call of Duty, Halo) just for being a girl. If I had a dime for every time I hear "shouldn't you be in the kitchen?" or "why don't you (insert sex act here)?" Beyond frustrating. Gears is the worst for that stuff, but in both CoD and Gears I've had players on the opposite team or even my team run around to specifically find and kill me, just because I'm a female gamer. Why? I don't know, but there you have it. I find the mute button works wonders.
But I do have to admit, the 5 year old in me likes the new CoD multiplayer partially so I can see all the ways people can figure out how to draw profane pictures on their badges. It really amuses me, and I know it shouldn't. There is a humor in picking up the gun of the guy you shot and seeing "F U" written on it. LoL But honestly, the new CoD online is awesome and worth checking out. It really levels the playing field a lot more than the old one did. But I was always a fan of the odd numbered CoD as opposed to the evens. Infinity Ward was fine, but I thought the game was so much better by Treyarch. And the stupid minigame on the main screen is addictive.