Rabbits as "foodies?"

   For many years, my wife and I have grown a large garden, and except for lettuce, kale, and other leaf crops, we've never bother with fencing out the rabbits.  We could plant 75 tomato plants and the rabbits would ignore them.   Then last year,  instead of just buying young plants from the local supermarket, we sent away for some "heirloom variety" seeds and started some of our plants from seed.  But we still bought some commercial variety plants.  But when the stuff was all planted, in one night, the heirloom plants were all eaten off to the ground by rabbits.  And the next night, they pulled up the roots and ate them too.  Yet the commercial cultivars, planted a few feet away in the same garden, were unmolested.
     So, what's going on here?  Do the commercial varieties have some genes that repel rabbits?  Or do the bunnies simply know what is yummy and what isn't?  I had always assumed that rabbits were fairly  indiscriminate in their choice of food, eating any edible leaves.  But given a choice, the bunnies are the real foodies--not we humans.