Normally I'm against helping folks with their schoolwork, but this is actually an interesting question.

I don't think there's just one answer.

One thing is that Adobe has embraced the highest of high tech in order to technically do things that others can't do, or which would be too expensive or time consuming to do.  This includes things like writing multi-threaded software, doing GPU programming (OpenGL shaders and Mercury engine), creating algorithms that use innovative math to achieve difficult tasks.

Another thing that comes to mind is that Adobe builds on proprietary libraries of controls that allow them to sell the same apps onto multiple platforms (e.g., Mac and PC).  Hardly anyone does that.  Pure Windows shops might be sweating over whether the next version of Windows is going to flop, but Adobe is just smiling because if folks flock to Apple, they're already there.

A big one that comes to mind is that they offer huge suites of applications that (more or less) work together to solve big problems.  Some people only need a photo editor, but others need to be able to edit photos, craft illustrations, work on videos, do web designs, make flash presentations, etc.

Adobe doesn't give much away, and their Marketing strategies are fairly shrewd.  Their product upgrade policies tend to guide people into buying each new version when it comes out.  Support essentially ends for older versions when new ones come out for example.  While there are ways to open your new camera's images with an old version of Photoshop, the most convenient way is to stay current with the latest release, etc.  And of course their new month-by-month software leasing targets folks who either can't or don't know they want to commit a lot of money all at once to buy licenses.

And they provide forums where they get people to answer other people's questions for free... 

-Noel