The reason plants are clone only is most likely because when doing the breeding, it was a special pheno that only showed up in the one plant, and they could not get the genes to pass down to the next generation. Some times you will get a freaky pheno that is only 1 in a million, and to get that same pheno again is near impossible. That is why you should always grow as many seeds as possible when starting from seed to make sure you get the best pheno possible.
Even if you took this special pheno and bred it with a male of the same strain, you will not end up with the same plant as the original. Now you can back cross it and end up with an almost pure strain, but it will never be the original. Take "Cheese" for instance. It was clone only, then it was back crossed and now is available in seed form. It will be good bud, but not the same as the original clone because it is not pure "Cheese".
Hopefully this cleared things up for you.