Ever since Shadowrun it was shown that cross platform gaming was possible.

With PC and Consoles growing closer and closer, why aren't there more Coop or PvP cross platform options?

I can see only benefits. I'm currently playing Dark Souls, which has an awesome MP component. But I'm restricted to the PC playerbase. I would love to team up with some GOGers for it, but they have it on the console.

And wasn't that a promise MS made with GFWL anyway?

Because any PC user will pwn every console-causal player with the power of mouse xP / trolmode off

I remember that Valve planed crossplay in new CS; but - both: PC and console player's didn't like that idea so this idea was scraped.

Which is really stupid, considering all you have to do is make it an option when setting up the server:

Console-only
PC-only
Mixed

That is actually a very good question, which I hoped the answer would have been easy to find. Unfortunately, it seems noone really knows why.

So, assumptions to get the ball rolling.

1) Competitive FPS will favor one platform over the others, due to that platforms input method (aka mouse instead of gamepad). Not sure if this is true or not, and I think more recent games have tried to fix it, usually by assisting the aim of a gamepad user. One could probably check that with DX:HR, since it has both control schemes, and one could have a few firefights and see which way feels easier.

2) Closed network platforms mean that it's harder to communicate and work with. I don't really see any problems here, since the developer would have to have access to the network code to program inter-platform multiplayer, so while it may be harder to code cross platform multiplayer, it shouldn't be impossible. At the very worst, add a flag in the start of the network code, and depending on flag, run relevant platform's handling.

3) Patching. We all know that multiplayer (almost) always require all parties to have the same patch installed, and that means that the patch should go out at the same time for all platforms. I think this one could also be circumvented, probably by having a major patch version (1.0, 1.1 etc) which is required for cross platform, and a minor patch version (1.1.1, 1.1.2) for bugfixes, thus ensuring that cross platform could still work, even if the latest bugfix isn't out yet.

As I said in the start, all of the above are assumptions, which may be completely off target, but I do believe that it isn't a technical limitation.

This would only apply for FPS anyway. Which are the more boring MP games anyway (at least for me).

What about the countless 3rd person action games that are designed for gamepads?

Microsoft tried integrating cross platform play when it launched the 360

Shadowrun and Universe at war were certain titles that supported this feature

Unfortunately the reason this was dropped so quickly was because gaming news websites reported that PC users "Decimated" console users and they "Had an unfair advantage"

yup, this is a nice option - especially just for playing with friends but in "pubs" PC players will only join PC-only, consoles, console-only and mixed will be populated when the other server's will be empty...

I'm fairly certain that any console player would have my ass on a platter if I go up against him in any game NOT FPS/RTS.

What about cross play with Steam, Origin, Impulse, etc.

But with diminishing MP that could be a life saver for a game. I personally have no problem playing with or against a consolero. But even if I had, it would always be better than NO players.

Thought so, especially seeing this thread pop up instead of a reply ;)
Btw, anyone has XCOM:EU on XBOX360 or PS3 so we can do a few tests about the multiplayer?

AFAIK they never talked about it or implemented it. Unlike MS.

(Mac/Linux/Windows is not really what I mean, more of a sub-section).

Dark souls comes to mind as a good cross-platform title.

That is exactly the game I'm thinking about.