I don't think that being a physicist gives you a passport for being a great developer (I am not, for example), but there are some very basic characteristics of physicists that are important to point out.
Why do physicists make potentially good developers?  
  1. mathematical knowledge
  2. a passion for solving complex systems
  3. the ability to work in a team, as most physics work involves large collaborations
  4. experience of basic programming languages (such as C#)
  5. computer science is just a special case of physics anyway :)
Re point 4: it is true that most physicists will not learn or use Ruby on Rails or Javascript for their Ph.D. work. To build a website or an app, your knowledge of Fortran (still wildly popular among astronomers!) will not really help. But by default, most physicists will learn C# or C++, as well as basic database languages, and HTML/CSS. Moreover, nearly all physicists (and astronomers) will compile their papers in LaTeX, which is, after all, a programming language? The next generation of physicists (some of whom are increasingly becoming data scientists) is more familiar than ever with Python and Javascript (e.g. d3.js). My view is that the gap between the computational skills of a computer scientists and a physicist is getting more and more narrow, as we enter an age where all of physics research requires data handling and computation. Physicists can code.