I'm a little vague on this, Dan, but I always had the impression that yams were actual roots, rather than tubers.
Other than that, yams and sweet potatoes are totally unrelated. Sweet potatoes are Ipomoea batatas, of the family Convolvulaceae, and their closest familiar relatives are morning glories. Yams are in the family Dioscoreaceae, which puts them three steps back on the taxonomic chain.
True yams are often available in Carribean markets, because they're very popular in the islands. But other than that, it's rare, indeed, that they appear in the U.S.
Personally, I've never been a fan of dousing sweet potatoes with syrups. They're sweet enough, as it is, and I go a different route. For instance, I do a major variation of a recipe that originally appeared in Vegetarian Life magazine:
Hazelnut Stuffed Sweet Potatoes
3 medium sweet potatoes
1 apple, peeled, cored, chopped
1/3 cup apple juice or cider
1/4 cup currants
1/2 tsp cinnamon
1/4 tsp nutmeg
1/4 cup yogurt or creme fraiche
6 tbls chopped toasted hazelnuts (filberts)
Preheat oven to 375F. Wrap the potates in foil and bake until tender, about an hour. Let cool.
In a skillet over medium high heat, cook the apple in the juice until softened. Stir in the currants, cinnamon and nutmeg. Cover and set aside.
Divide the sweet potatoes the long way, and scoop out the flesh. Put the shells in a baking dish and set aside.
Add the apple mixture and yogurt to the potatoes and mix well to combine. Fill the shells and sprinkle each with a tablespoon of the chopped nuts.
Return to oven and bake 20 minutes or until heated through.