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I think he's referring to the information you create based on their source you saw; who ends up controlling it when you publish code that looks an awful lot like theirs under the GPL? How much will you be sued for?
And the next problem: Microsoft doesn't have to let you look at their code. Their shared source is for private modifications, educational, and that sort of thing. They're not going to give it to you so you can interoperate with their stuff: They don't want you do.

These things actually extend far beyond the server issue. Kerberos is used to login to Windows domain servers: It's needed to setup clients to login to Windows domains. Or to setup servers to act as Windows domains with the clients.
SMB is used for all filesharing under Windows. I think Samba has pretty well reverse engineered it (when it fails I'm never sure whom to blaim, the bad serverless design or the broken reverse engineering).

LDAP is also something needed to create clients.

The problem is with Microsofts "embrace and extend" policy when it comes to standards. There are two correct ways to extend a standard: Propose the extension as an addition to the standard. Or, don't claim to be standards compliant.

I'm not convinced they really should have to hand over source, or even documentation. But I do think their attitude towards standards has been extremely pathetic and everyone buying their software should be well aware of the lock-in they face.

Don't keep saying they aren't a server monopoly, we know. The problem is that they are a client monopoly, and these protocols are used for communications with clients. It's pretty tough to changeover ALL of your client and server stuff at once; and doing it slowly is expensive (redundant servers, slow communications waiting for reduncant servers to merge, etc).