That comparison seems weird because the relationships aren't the same. Comcast's customers are the people who pay for Comcast service at their homes and businesses. If Comcast favors its own content over other content, and they have a local monopoly on internet service, then they are using their monopoly to abuse their customers.

Neither Microsoft, nor owners of Windows Phone handsets, are customers of YouTube. The only people who are customers of YouTube are people who pay to have their videos hosted there.

Is YouTube purporting to provide me with Internet access or otherwise operate as infrastructure? I must have missed that.

If Comcast wants to provide a digital network that provides connectivity between selected entities (such as end-users and companies that have elected to pay Comcast additional fees), that's fine. But they don't get to call it "Internet". They don't get to pass it off as something different from the AOL and CompuServe of old.

Comcast and many cable ISPs have a monopoly for high speed Internet in many parts if the US. YouTube is not forced on anyone due to where they live, and there are plenty of alternatives to YouTube out there that you are free to use.

There are no "others" and no "rules". Google makes the iOS and Android apps, not third parties. The Windows Phone YouTube app would be the first significant (1) phone OS to have a YouTube app not made by Google, there are no others to compare Google's behavior on for fairness. This is the first event of its kind.

(1) If you consider single digits market share to be significant.

Why?

How is this any different than me releasing my code under something like the LGPL, which would allow those folks who dynamically link to not release source to their app, but force those who are required to statically link (due to platform or other reasons) to release source to their app?

Note that it's a similar situation. If I release code under the LGPL, i don't have to abide by it, only others do.

Twitter requires third party API users limit themselves to 100k users (or whatever it is), but, even though they use the same API, does not require it of itself.

They also have decided some folks don't have to abide by this.

How is this different?

None of this is "anti-competitive" behavior.

Would you think it anti-competitive behavior if Google provided no API and also told people finding ways to embed it to stop?

HTML5 seems to be the only public API they expose, and obviously they don't want random apps to depend on other, possibly undocumented APIs intended for internal use. Google can use any kind of whatever internal API they have in place in their own apps, I don't see why they should follow their own third party usage guidelines.