depends how hard the hard case is
it'd have to be a solid box that doesn't fold no matter how much pressure you put on it (within reason), but that'd make your pocket book rather bulky
a simple leather wrapping won't help much when you have your pocketbook in an already bursting backpack and you get pushed around on the metro... the device is just plastic and when you put stress on the entire device, the screen is the first thing that pops
Like any other piece of electronics, ereaders are breakable devices and you should treat them as such, so don't just stuff them somewhere