For all intents and purposes, I would say using them interchangeably is not a mistake. At least I would.
Now if you really want to dig deep, など is simply adding additional emphasis.
The translation is going to sound weird (because, again, they are pretty much the same), but to give you a rough idea:
- スーパーには、りんごやナシがあります。In the supermarket, there are apples and pears (and so on).
- スーパーには、りんごやナシなどがあります。In the supermarket, there are apples and pears and so on (you're explicitly stating it).
Additionally, など carries the nuance of 例えば (for example):
- スーパーは、りんごやナシがあります。(neutral, but implies you have other things too)
- スーパーは、りんごやナシなどがあります。(for example you can find pears and apples, explicitly saying you have other things too).
The 大辞林 第三版 states:
Which highlights the role of as emphasis in a sentence. I would add that it is mostly a word you will see written / used in formal situations, and one could argue that it is sometimes (overly?) used as a "stylistic tool" of writing (〜や〜など sounds more formal than 〜や〜).