[NerfedWar]

With regards the names of products/addon, we're dealing with trademark law and this differs quite considerably between countries. There is no such thing as an international trademark (although there are a couple of treaties that work around this limitation for ofiicailly registered trademarks).
The common-law Trademark (poducts not officially registered with the official trademark office of a country) is pretty much impossible to enforce across borders and is not even recognised within the borders of some countries.

Addon hosting sites may/should likely take a more conservative position so that they don't get bogged down in such arguments between authors.

With regards the capabilities of an addon and writing an addon with similar capabilities ...brings to mind apple/samsung... We're not taling about copyright here, but patents (and other less tangiable things). I really hope we can be sensible and we don't end up with something reminicent of the mess that is the US patent office... Either way, there is no possible way an addon author could enforce such across borders (unless it's a commercial addon bringing in millions...).

Again, addon hosting sites may want to take a conservative position just to keep out of any arguments between authors.

It would be polite to ask the previous author if you can reuse a name though... or tell them of your intent.