Question
The way I understand "deadheading" is to pinch off the shrivelled petunia bloom BELOW the part where the seed head will form.  A friend merely pulls off the faded blossom, leaving the seedhead to form.
Some petunias don't seem to form seed heads but just frilly looking leaves where the blooms were. Is this just by chance or specific to certain varieties?  I generally purchase "sale-at-big-box-store" petunias so I can't document what kind I have.  thanks!

Answer
J,
Yes, you are correct and your friend is wrong. You deadhead petunias by snipping the stem below the spent flower, thereby removing the developing seeds. For most flowers the entire point of deadheading is to remove these seeds as the plants will keep making flowers if they are still on a quest to make seeds.

Super Petunias (Proven Winners) and Wave Petunias (Ball Horticultural plants) do not make seeds and don't have to be deadheaded. I have never seen these in six packs, only in pots, so if you bought petunias in six packs you have the ones that need deadheading.  Super Petunias and Wave Petunias are always labeled as such.

I hope this helps!
C.L.