Question: This question [Kiel traduki Esperante tiun ĉi ludkarton?](https://esperanto.stackexchange.com/questions/2486/kiel-traduki-esperante-tiun-%c4%89i-ludkarton) requests a translation of the text of a playing card, not any specific word or phrase. Is it outside the topic for this site?

Answer: 
word-difference: you ask for the difference between **words**

word-choice: you ask which word you **should** use in a **specific context**

The emphasis can be very different. With "word-choice" you can ask opinion about if the word is uzinda or is useable in a specific context. "word-difference" is much more about the meaning, and not the usability and uzindability.
No, since they aren't synonyms. [word-difference](https://esperanto.stackexchange.com/questions/tagged/word-difference "show questions tagged 'word-difference'") is for questions asking about the difference between two words; [word-choice](https://esperanto.stackexchange.com/questions/tagged/word-choice "show questions tagged 'word-choice'") is for questions about which word should be used, given a list of words.

Clearly, since Stack Exchange sites expect well-scoped questions, I would generally expect [word-difference](https://esperanto.stackexchange.com/questions/tagged/word-difference "show questions tagged 'word-difference'") questions to make clear in which context the OP is asking; questions should not be about the difference between two words in general, since that would probably make the question too broad and less or no helpful to future users (which is the target of any Stack Exchange site, together the user who asked the question).  

In the same way, [word-choice](https://esperanto.stackexchange.com/questions/tagged/word-choice "show questions tagged 'word-choice'") question should not ask for choosing a word from the full dictionary; the OP should make clear which words they think could be used.