It's only required for trademarks. Copyrights and patents don't require defending every case to maintain ownership.

Perversely it might actually be a good thing if you did have to for patents as it would force trolls into the open early on (ie before their claims run into the millions).

This is only partially true. You are 'strongly encouraged' to enforce your patent violations, for after a period of years (6) they basically become unenforceable. This is to prevent things like 'patent bombs'.

In practice it doesn't always work this way ( see patent trolls ) but it can be a BIG issue for people looking to enforce their patents.

Here's an interesting example:

http://www.ipwatchdog.com/2010/05/26/estoppel-time-bomb/id=1...

No, that is only true for trademarks, not for patents or copyright.

And this confused comment is a good example why the FSF recommends against using the confusing term "intellectual property".

No, that ALSO applies to patents, though the term is actually 6 years rather than the standard 3. Your 'confused' comment is a good example of why the FSF should encourage educating ones-self instead of trying to play semantic games with the english language.

I assume you are talking about this, which mentions a 6 year limit:

https://www.law.cornell.edu/uscode/text/35/286

But that only limits the time period for which damages may be claimed - it does not forfeit the ability to claim damages altogether, which is what may happen with trademarks; that's a pretty significant difference.

Ok, that is an interesting aspect of US patent law I wasn't familiar with. But this doesn't look like a universal property of patents, more likely it's specific to the US?