The key difference is the crust: while appeltaart is made of some weird doughy mix that's neither a pastry nor a cake, apple pie is is a real pastry crust, made with way more butter than is good for you--and a touch of shortening (found in a rare toko) for extra flakiness. It's easy to handle, which is fortuitous because you don't want to let it warm up, because otherwise the fat starts oozing out and you loose the flakiness. And it's fast--just a quick whizz in the food processor and it's done. The difficulty in pastry crust is that you need some Fingerspitzengefuhl for when it starts to come together, and know to stop the food processor before it does. Pastry dough comes together during its rest in the fridge--it's the fact that it's not together before the rest that makes it so soft and easy to handle.
But the main reason I don't make apple-baked-goods in general is the enormous amount of peeling, coring, and chopping involved. Truth be told, it doesn't actually take that much time to do it--about 40 minutes for the huge-ass quantity of apples that a pie requires--but it's still a lot of work to be done in a short time. Yes, I sprinkle lemon juice over the apples to keep them from browning, but even that wears off at some point.
Still, there is something to be said about pulling a beautifully-crisped, golden-brown, steaming and bubbling apple pie--or appeltaart--from the oven. Baking in general requires a certain faith in your ingredients--that the dough is developed enough, that the ingredients will behave the way you expect them too. Part of the excitement can be contained with enough practice. But the whole endeavor is unpredictable enough to warrant a prayer or two, and always brings a sigh of relief when it goes well.