Difference between a Prog/analyst, Software Developer, and Software eng.

I was looking at the recent Computerworld IT salary survey and noticed the following entries along with total compensation (average salary plus the average bonus):

Programmer/analyst ? $71,544
Software Developer ? $79,069
Software engineer ? $89,770

So could you tell me, just what is the difference between these 3 occupations?

Obviously one huge difference is pay, but to me is seems the titles could be interchangeable depending on what your company wants to call you. I started my career with the title of Software engineer, but then moved to a new organization as a Programmer/analyst. Now I consider myself more of a Web Application developer, yet my title is completely different.

So what do you think, are these pay differences justified?