Remain alert. Here's the fundamental problem with Microsoft's otherwise praise-worthy announcement.
Any right that can be granted, can also be taken away.The U.S. Constitution does not say the federal government "grants" rights to the people and the states. It says those rights are inherent, and that the government exists to guarantee those inherent rights. Why? Because any right that can be granted, can also be taken away.
Microsoft says they won't sue, in other words they imply that they are granting a right to other developers to use the software specifications. Well, whoop-de-doo.
Compare this with the GPL, which explicitly says the rights to use the software are inherent and the GPL guarantees those rights.
The analogy should be obvious. Any right-thinking American should immediately see that while Microsoft is doing a nice thing in this instance (granting an implied right), they are not doing the correct thing, which would be to state explicitly that the right to use is inherent, and that they will guarantee it.
Nevertheless, good for Microsoft. Given where they were only a few years ago, we should be pleased. They've taken one small step away from doing intentional harm.
You make some excellent points....