Why are all app screenshots taken on Mac/Safari?

Why all web app screenshots are depicted as if they they are taken on a Mac? I sell a desktop software aimed at photographers and Mac sales are not even 10% of Windows sales! People who pay for software seem to be using Windows but since it is considered cool to develop on Mac, developers put up screenshots of Mac. Why nobody puts up a screenshot taken on a PC or that shows some other browser like Firefox or Chrome or even IE?