That's an odd way to justify or explain release of the source code.
What I believe they ought to do is accompany it with documentation about the designs of those codes and discuss the evolution to the points where they either ended or evolved into what they are today. DOS is obviously gone as far as Microsoft is concerned unless they consider their command prompt the current incarnation of it. Word is obviously still around, I get that it's proprietary, but if they're releasing version 1.0 of that code (1) it's probably a lot of code, and (2) to benefit academic learning it would be beneficial for them to at least make an effort to document the code architecture as opposed to simply releasing it to a museum and claiming this is for the children.
For that matter, how about releasing a description of the first BIOS and how DOS tied into it? That's just as important as the OS itself.
Otherwise just handing out the code is pure PR and looks good, but if someone has to decipher the design (a) they may make invalid assumptions and (b) they may may not be able too, leading back to condition (a) where they'll "make it up".
The whole point here is to incite historical learning to benefit those studying computer architecture. Much the same as why computer scientists learn about Turning machines or Moore and Mealy FSMs. In this case it would be so that someone would have a background on how the first operating systems were constructed, the pitfalls of them, and what options could've been chosen to have made that better. Much like you read about old operating systems or designs which were actually very good, but didn't take off from a business sense, so they never made it. Microsoft can tout a lot of the line that they did and were successful. OK, they have their kudos and the money to boot. But some coverage of how it was constructed to go along with "here ... have some code" would be helpful.
Perhaps they are releasing documentation to go along with it.