Earlier quoted context omitted.
It's not a "pretty minor violation", that's the only condition of the MIT license. Yes, they mentioned Spegel, but only to thank the authors for "generously sharing their insights" -- that's not even close to the required statement that part of the project is owned and copyrighted by the authors of Spegel.
Ok, so MS will see this thread and re-add the missing header to a few files. You really think the author is going to then feel 100% better about it? They are just another data point in the long list of authors who chose a permissive license and are then shocked when a billion dollar company takes advantage of it.
What I'm not OK with is a company doing that without attribution. If XYZ company's product is built on code I wrote, I want to be credited -- both so that I can show it to potential employers, and so that users of XYZ company's product are aware that some of the code in it is something they can use for free and modify for their own purposes. If the attribution wasn't important to me, I would have chosen CC0 instead of MIT.
So yeah, if I was the author, I'd probably feel a lot better about if MS re-added the correct attribution. I'd probably still feel miffed that they tried to pull one over on me in the first place -- but I wouldn't be offended by the fact that they're using my software.