Many hardy
trees do need stratification but not all. It also depends in varieties. But yes, stratification is mandatory for some species.
The seeds of apples from the supermarket (common varieties) can germinate at room temperature. But siberian
apple does need stratification for example.
Also, the duration of stratification varies WIDELY! And how it is done.
Good king henry or wax myrtle, hardy perennials, need about 3 weeks of cold moist stratification. Trees like silverberry need 1 to as few months. Some species need longer. Some species still germinate without stratification but germination is enhanced by it (crambe for instance). This is just my empirical experience.
Lettuce and asparagus do not really need stratification but benefit from germinating during or after a colder period, and 10ÂșC is just around fine. But species need a colder shock.
Some species even need cycles of alternating cold and mild weather. Some species germinate well after a period in the fridge in a moist paper towel or in peatmoss within a plastic bag (for example, pecan, almond), but other species do not work like this (good king henry for example).
Furthermore, some seeds of same species readily germinate after treatment, others wait a bit longer. This ensures germination at different places and conditions, and enhances survival.
Also, seeds enjoy germinating in their most natural conditions. Sometimes seedlings might suffer or die, when they germinate after a cold treatment and are moved into a
greenhouse, rather than been allowed to follow a natural gradual increase of temperature outdoors.
There are several species that I am still trying to cold stratify in order to be able to germinate them but so far I had no germination yet : walnuts, hazelnuts, aronia, amelanchier, and many other species.
Finally, it is possible to cheat and by using hormones, to
skip cold stratification, though I have never been able to do that.
Seed germination can often be a tricky business but it is a really rewarding thing once you achieve it!