I would be very surprised if the profit on that one sale would cover certifying the product and supporting it going forwards.

What technical reason would a server company have for NOT supporting a largely standards-compliant browser like Opera? Isn't the whole point of serving up content to the World Wide Web to be able to communicate with multiple devices all over the world?

Is it impossible to write a Web application that simply doesn't test the limits of most browser implementations? Again, I'm asking an informational question to follow up on your interesting response. What actually happens in the typical case of a server vendor's application that is supposed to run on an arbitrary browser if a browser the vendor hasn't considered is used? Does the whole application crash? Or does it just look a little bit less pretty?

Unfortunately, you don't know which of those end results you're going to get until you actually try the thing out, and the answer could be wildly different on different pages of your app.

It's still generally poor form to straight up disable a particular browser unless you know for a fact that it doesn't work properly (generally in the sense of you-can't-use-the-site, not things-look-kind-of-funny), but perhaps in this case they did in fact know that their app didn't work with Opera.

Your assuming that value amounts to a large portion of their revenue.

I'd venture it doesn't, and they wont be too worried.