Yup, that is true.  If you want to grow a variety of much of anything it is best to buy at an organic market, see if you like the taste and then propagate from there. 

In the case of potatoes & yams; they are perennial vegetables.  If you successfully grow them in a spot, leave a couple in the ground and they will pop back up and thrive the next year---repeat forever.  And they will break up your soil for you in the process of growing.  Make the plants do the work, cuz they want to.