Rugelach by any other name would, after all, taste as sweet.
Or would they?
The rugelach most of us (Americans) know today are the product of the industrialization of cream cheese which, according to the venerable Wikipedia, occurred sometime in the latter half of the 1800s. This article traces the early history of American rugelach, beginning with Kraft's role (which acquired Philadelphia in 1928) as it introduced a cream cheese dough at the 1939 World's Fair in New York. It was, of course, the zeitgeist of the time for companies to make it their business to find convenience-making, time-saving shortcuts for women so they could take advantage of all the new-fangled appliances in their modern homes. It is no wonder, then, that a quicker, simpler dough would make baking rugelach seem a more accessible task, one that could more easily fit into a modern woman's day. Soon after the World's Fair introduction, Kosher bakeries on the East Coast began to include the cream cheese version in their offerings. It is this version that is ubiquitous in Jewish and non-Jewish bakeries alike, and beloved by all who come across it.
The Americanized version did not spring out of nowhere. It is a modified version of a pastry that had been enjoyed by the people making it, and their parents and grandparents and so on, for generations. The origins of the pastry are debated: after all, rolling a dough with a sweet filling is hardly a revolution in culinary creativity on anyone's part. It is similar to Polish, Russian, Hungarian, Austrian, German, and numerous other regional specialties. But regardless of where it came from or who was making it, we can be fairly sure it was yeasted (of course before the commercialization of yeast, which at the earliest came around 1780, "yeasted" means risen with some kind of starter), and likely had sour cream and/or another thick, rich dairy product, depending who was making it where and at what time. Such yeasted rugelach can still be found in some enclaves in the U.S., as well as abroad. They are not as flaky as the cream cheese version (which has a much higher fat content so because of science causes more flaking in the dough), but they are instead softer and chewier.
So what makes a rugele a rugele? It is not likely the dough, or even the fillings. Walnuts, poppy seed, fruits, and cinnamon are all common and traditional fillings, and that repertoire has expanded to include chocolate and even Nutella and more for the particularly adventurous. And as we now know, there are at least two styles of dough that would be widely considered appropriate, and while the proportions for a cream cheese dough are pretty much universally standardized, there are infinite numbers of ways to make a soft, sweet, high-fat yeasted dough. Many bakeries even use laminated doughs (like croissant dough) to make their rugelach. One could use strudel dough if one was so inclined. There is nothing in the dough particularly that would identify a pastry as a rugele or not. And the bounds for possible fillings are pretty much constrained by (1) sweet and (2) kosher.
I'd argue it is partly the shape of the rugelach that make them so. A small triangle is rolled from end to point to give the distinctive shape. Some try to pass off the "easy way" of making rugelach as a legitimate alternative: rolling like a jelly roll then slicing and baking on a tray. But this is the wrong shape, and don't let anyone tell you otherwise. After all, making rugelach can't be too easy, because what reflection of the world would that be? Our food traditions come as a reflection of our experiences, and process and shape are all significant. We may not know what the shape signifies any longer, but far be it from us to go changing it. You'd hardly accept a cinnamon roll without a swirl, so you can't accept a rugele that was never a triangle.
It is also the name that makes it itself. The words we call things give them meaning and context beyond the literal and obvious. By calling them rugelach instead of "crunchy nut treats" we place them firmly within Eastern European Jewish tradition (for those that recognize the name), and as a food on loan from somewhere else (for those that don't). We can also attach memories, feelings, and more to the words we say; rugelach are comfort food. They remind us of our mothers or grandmothers in the kitchen, or of treats we shared with friends and family on holidays or special occasions.
Without our shapes or our words, we risk these connections to our collective pasts and we lose the identity of our foods. A rugele without a shape or name is a lonely treat indeed.