Perhaps the comparison was a bit off. I am not intending to be argumentative in the slightest.

Microsoft's context for .NET is only broader due to community effort and NOT due to Microsoft's active help. When .NET first came out, was it as widely usable on all those platforms and for different types of applications? No, and that's exactly the position that Swift is in right now.
In a few years time, there might be a community effort for Swift on different platforms, but look at the success of GNUstep and the libraries surrounding it; there is not wide adoption by any means yet Obj-C remains popular.

A large portion of the list of applications that you mention are typically Windows platforms - Windows desktop applications, Windows Store applications, web applications on Windows servers, Windows phone apps. Replace the word "Windows" with Apple or iOS and you get the complaint that the parent mentioned. It's entirely a point of view problem, ie you don't get iOS/Mac OSX developers complaining about new language features in T-SQL when SQL Server is not available for iOS/Mac.

I suppose the same complaints were made against .NET all those years ago - "why bother learning it? I can use the libraries and languages I already know!". It is a poor complaint to make really, as the effectiveness of a language or library does not depend on it being open source, eg. Java (years ago), the Win32 API, MFC, Carbon, Cocoa, C++ (does the committee steer itself based on our suggestions we just throw at them?). Their success and use has happened on closed-source platforms and with closed-source devices, but it's entirely irrelevant in the same way that adoption of an open-source language is, surely?

It would be interesting if Apple does open source Swift, but as you say they won't promote Swift outside Apple apps (in the same way that I can't see that much marketing material from Microsoft encouraging us to use Mono on Linux; ie, Microsoft doesn't promote .NET use outside Windows platforms either). But that doesn't stop an army of C# developers existing.
It would be interesting to know how many of the C# developers use that language because it is available on multiple platforms (perhaps we could have a poll?). I would think that very very few developers are using because they know it is cross-platform to some extent ("I'm going to use C# and .NET for my Active Directory MMC snap-in page because I can attempt to compile it on another platform!"); in fact, C# and .NET jobs mention Windows development 98.9% of the time don't they?

I just thought that refusing to even take a look at a language due to it not being open-soured was a bit of a foolish thing to do or complain about, and to be upset that a language (designed by a company for its own operating systems and own devices) was not available on other platforms and OSes was a bit of an odd complaint to make too!

EDIT: I have reread this and it sounds quite harsh! I don't mean it to sound harsh. I did not know that Microsoft has opened up the .NET system a bit; I was more attempting to highlight that the original parent's comments was a bit whiney for no reason, and I wasn't meaning to pick a quarrel with you btw. Apologies!