Windows Phone has a very small market share. If we discovered that people running Opera on Maemo (if there even is such a thing) are getting the same behavior, would it surprise anyone? Would anyone even object?
They don't have an obligation to support tiny platforms that would cost more to support than they're worth just because Microsoft is very loud to complain about anything they do. Or subject users to a crashy experience because the site doesn't need Webkit to load but still needs it to not crash. Any more than Microsoft has to make officeupdate.microsoft.com support Firefox on Mac rather than just redirecting it to office.com like they do now.
As a matter of fact, they do try to block Opera aggressively from their Google Apps. Gmail on Opera (Linux version only) will force you to use the HTML-only version of the site, while display a message telling you to switch to a more modern browser (even though Opera is usually the most standards-compliant browser at any given version compared to its rivals), linking to Google Chrome. I searched on the internet for this, and it seems to happen to non-Linux machines too, but since reports of it are so scarce (Opera is probably the least used browser out there), no one seems to care.
I'm very saddened by the results of the antitrust motion and I hope they get cornered again on antitrust issues. Google and Apple are the new MS, really.
OK, so they discontinued it. For many years windowsupdate.microsoft.com and officeupdate.microsoft.com were Internet Explorer requiring websites with Active X controls to update the appropriate Microsoft software. No support for Firefox on Windows and no support for Mac at all. How does the fact that they discontinued the website itself make the example less valid? It still happened. And there are plenty of other examples from across the industry, if you're actually questioning that.
Anything that still uses Active X is IE-only. It has been slowly dying, but it most certainly still exists, and for many years (even fairly recently) Microsoft was one of the major perpetrators. And Silverlight is almost as bad (but thankfully much less widely used). Half of Apple's web services only work or work fully with Apple's operating systems. There is no Mac OS X support on Amazon EC2 (you can certainly blame Apple for that more than Amazon, but then you're just blaming Apple instead of Amazon). I'm sure you're aware of the kerfuffle over Microsoft shoving proprietary "do it like this version of Microsoft Office" specs into the OOXML standard over strenuous objections by competitors. Almost all of Microsoft's server products rely on Active Directory for feature completeness and don't play half as well with non-Microsoft implementations of LDAP or Kerberos.
If competitors had an obligation to support competing platforms then you could find no saints in this industry.
Edit: Incidentally, I'm really enjoying the irony of you loudly and repeatedly complaining about people downvoting pro-Microsoft content (notwithstanding that this story has remained on the front page for almost a full day) while your brethren simultaneously downvote my comments instead of responding to them.
They don't have an obligation to support tiny platforms that would cost more to support than they're worth just because Microsoft is very loud to complain about anything they do. Or subject users to a crashy experience because the site doesn't need Webkit to load but still needs it to not crash. Any more than Microsoft has to make officeupdate.microsoft.com support Firefox on Mac rather than just redirecting it to office.com like they do now.