Are comments like that really necessary?

Necessary no. Hurtful? I don't think so, if I may say so myself.

It's a comment to put into perspective the relative insignificance of the platform -- and thus that the statement of the parent that it supported that too doesn't amount to much.

It also shows how MS effort was either badly thought out from the start, or at least failed -- and all those cross-platform touch-first changes of Windows UI where later toned down.

Sure it is. We must never forget that one of Microsoft's biggest selling points for UWP, and by extension the Microsoft Store, was to port apps to a platform that was, frankly, dead on arrival, at a time when the vast majority of Windows users were using mouses and keyboards.