In the USA, prisons are classified by security level. Here’s a rundown for Federal facilities. Alderson, where Martha Stewart did her time, has indeed been called “Camp Cupcake.”
Martha Stewart was sent to Alderson because she’s neither violent nor an escape risk. And most of the other prisoners were neither rich nor powerful. (She’d actually requested a Connecticut prison, to make it easier for her elderly mother to visit–but her request was ignored.)
White collar criminals aren’t sent to the maximum security prisons because of the nature of their crimes. But even the “best” prison in the USA is hardly a country club.