Frankly, this is both ridiculous and totally unnacceptable for our overlords not to provide this with multi-platform/browser access.
Its a frequently occurring problem.
The developers know the client will be testing on IE because that's what's installed on their corporate desktops, the client doesn't know any better and doesn't spec for multi-browsers.
As a result, the developer has an easy job.
You see, the problem with multiple browsers is that all browsers interpret certain aspects in a different manner (primarily related to layout). Its not rocket science to work around these little niggles.... but it does require a period of code tweaking and testing.
In the case of IE, it might also be the case that the developers have existing code they want to re-use that's written for proprietary Microsoft technologies (e.g. Silverlight etc.).
Yes, I know IE has the largest market share due to its inherent availability on Windows. But I agree that in this day and age, on a commercial project, its pretty much unforgivable not to at least provide some degree of cross-platform compatability.