[shkm]

I've really never had issues pulling almost entire instances as far as mob resets go. Indeed, Cathedral farming is typical -- though rather pointless nowadays, in my opinion -- as you can easily pull all of the inside simply by touching the boss, but you can really pull all mobs in just about any instance with some extra effort. If anything, resets are rare or the result of a bug because instances are simply not designed to allow you to outrun mobs.

If horseback is really the thing here, then there are indeed very few places within an instance; BM is one, and you could always count some old raids. Ultimately, though, the number "20" was just used for the sake of an example.

In any case, it's good to see an addon having come out of the discussion so quickly via Yourstruly.