you can do cold stratification outside the only problem with that is there are many many more things that can make the seed not sprout. i do all of my cold stratification in an unheated greenhouse. this keeps critters out, frost off, snow off, wind off, slightly warmer daytime temps. overall giving me a better germination rate.
that said when im doing seeds that i have a lot of, ill just do it outside and i get good enough results. but when im dealing with seeds that i paid for or only got a few of. i take the time to do it right.
if the seed needs the cold to germinate there is no point in not doing it, unless you feel like waiting longer or buying more seed.
The ultimate goal of farming is not the growing of crops, but the cultivation and perfection of human beings. - Masanobu Fukuoka