I would not say they prevent hackers from getting in your computer, dont rely on security through obscurity.
older apps can run faster, since they dont have all that extra fluff in them, check out how fast a CLI app runs. run some older win3.1 apps on your system. then again, those apps were created on older hardware, such as 386,486's, so they should fly on todays 6/786's.
older apps still fill a spot in todays software market, thats for certain.