True in many ways. There are many programs written for XP that still work fine on Windows 8. This is definitely a major advantage of using Windows as a platform. Personally, I’ve migrated back to OSX after a long time on Windows, and am quite happy, so this trade off is not as big of a deal for me as it once was.
However, there is no doubt that Steinberg developers have to deal with this OS update issue more often with OSX than with Windows. But on the other hand, I’m sure there are areas that Steinberg has to deal with as well on Windows that they don’t have to deal with for OSX. For example, QA testing the glut of other types of hardware that can come on a Windows machine. It’s an infinite universe that is constantly changing on the Windows hardware side, and Steinberg no doubt has a longer QA process for Windows against a larger combination of hardware components and their drivers compared to what they have to do for Macs. So I bet this balances out in the end.
And besides all that, Steinberg wouldn’t do any of this development – for either Windows or Mac – if it weren’t profitable. Clearly, at some point, someone at Steinberg has done their spreadsheets and worked out the cost to support both Mac and Windows, and the numbers from the accounting department must conclude that they’re profitable. 
So as long as Cubase users keep paying to use Cubase on a Mac, and those who use Windows keep paying for Windows, and the accountants say they’re bringing in enough money, then I don’t think it’s a problem.
Now if we could convince Steinberg to support Linux. 