I imagine he's pointing out that MS may not care about the licensing or lack there-of of old products like DOS. Although I've also never seen any statement other than the unfortunate lack of legality behind the "abandonware" concept. Obviously there are plenty of companies that make their only primary dollar on buying old licenses and suing everyone who uses the technology afterwards. In an ideal world obviously I think most would agree, a product no longer for sale is no longer making revenue and costs nothing to give away but anyway lawyers don't like the word free, they like the word license.
Not to drag the topic off too much but it's much like the interesting battles of the first mp3 sales. Companies pretending that it's the same as you buying the CD for a close to similar price, then one person arguing the flaw put his mp3 for sale on ebay and of course it got removed. Argument was it's the same as selling a CD or did the EULA that folks are being sold on not really apply. Certainly interesting as we go into more digital eras. I mean can I sell my downloaded copy of a game from Amazon or Steam? If not then what's the value when the price isn't usually that much better, plus if they terminate the service then where is my money/game?
Um, back on topic though and similar to previous answers. The best way would be to get a legal/physical copy from someone then you probably have the "Rights" to have a back up copy from somewhere in the event the disks are no longer working.