Most studios want to go multi-platform with their own IP if they can. If a third-party developed game isn't multi-platform then they are either being contracted to work on a joint project or they cannot yet finance a game on their own or make a deal with a multi-platform publisher. Working on a first-party project for a third-party developer can be a great situation but most studios would rather own the IP they came up with if they can. It just means they need a lot more money upfront and that they're taking a bigger risk.
I have absolutely no ill-will toward any developer that wants to go multi-platform with select IP and going multi-platform in no way means that a developer will no longer work on first-party titles. The people who run Sony and Microsoft are business-people who understand that and it doesn't mean a close relationship will suddenly end.
Anyone who makes a big deal out of this, in either direction, needs to get their perspectives in order.
