You don't know what you're talking about. I've been running simulations in C++ all my life, and I couldn't be happier with OSX: it runs on top of BSD (a Unix flavor, like Linux), which makes scripting a doddle, and has a free IDE with all the graphical dev tools to add interaction and visualization to the simulation program. Mind you, that part doesn't come for free. The availability of other, commercial software puts OSX a notch above Linux. Nowadays, you can install Cygwin and get the free Visual Studio edition for Windows, but for years, OSX has been the best dev platform around.
> Any entry level laptop will have more CPU and GPU capability to do whatever she's gonna be asked.
Simulations require so much CPU, you've got no idea. I had one of my first simulation programs run for two weeks over the Christmas holidays to get a decent set of parameters. More power is simply better in this case. Remember that optimizing simulation programs is far from trivial and will take a significant part of the PhD.