If I remember my biology correctly, each new generation of multicelled life creates differentation between the parent and offspring. This provides genetic diversity. This would be true in plants and trees as well as animals.
Anytime you want the identical charateristics of the parent plant you must produce a clone, most commonly done in bonsai through cuttings or layering.
Seedlings are often remarkably similar, some even have identical characteristics to the naked eye. This is mostly found in self pollinated species seedlings, such as an isolated green species Japanese maple trees, Acer palmatum. Growers seek out such trees for propagagion purposes for their consistency. Same is true for trident maple, Acer buergerianum. Some perennials are so consistant that even seedlings carry the cultivar name, although this is the exception rather than the rule. Consistant seedling variants may also gain recognition such as red Japanese maples, Acer palmatum var atropurpureum.
My experience with flowering quinces is that they cross pollinate very easily, so that if you have more than one cultivar in the area, you can be certain that the seedlings won't be similar. This is how I obtained the cultivar Chaenomeles 'Contorted Salmon Pink'. Japanese maples will very easily cross with Full Moon maples, Acer japonicum, for some interesting offspring.