As far as I know, yep. Wieso seems, to me, more like our "how so?"
"How so" is it that we can...
Why is it that we can...
I personally feel "wieso" adds a little something to the question, but I couldn't say what, ... perhaps it emphasises the subject of the question, ... not sure, but I tend to use it when I'm stressing the "why" questions, or if it's on its own, ... I feel "Wieso?" is better on its own. Dunno what it's like from the PoV of a German person, but I'll be sure to ask my German friend later; I'm fairly sure I did ages ago, and I'm fairly sure he said that both work, but I'll ask again to be sure.
I see you can manage with Spanish, so, I hope this helps: "Warum" sería "por qué", para preguntas estándar, sin embargo "wieso" tiene un ligero tono de extrañamiento, como para algún hecho inusual, por ejemplo, si has quedado con alguien y no se ha presentado, podrías usar "wieso", para frases como: "¿Cómo que (wieso) no has venido?" :)
Ah ya, eso tiene sentido. ¡Muchas gracias! Déjame repetirlo en inglés por si a alguien más le interesa.
Apparently, while "warum" is used as a standard "why", "wieso" implies a degree of disbelief or surprise. For instance, if you've arranged to meet with someone and at the very last moment he doesn't show up, you might say "why aren't you coming?" in the same tone as "what do you mean you aren't coming"? Here, you might want to use "wieso".
Thanks everyone for your answers!
You can use either one. There is a small difference, however. "Why didn't you come" would be said after the event is over, whereas "Why haven't you come" would be said during the event. For example, if you and your friends are at a party and one friend is late, you may call them and say "Why haven't you come (yet)?", but if the party is over and that friend never showed up, you could call them and and say "Why didn't you come?"