The "!Bang" page confused me for quite a few seconds. I have buried in some old memory layer the use of "!" as logic negation prefix (for plain ASCII typing), e.g. x = !y Curiously, I'm OK with the Unix shell "!cmd" to repeat ...
Heh, you think there is a better way to explain it?
Looking at it, seems to me you're conflating two things, with the confusion evident in the first two sentences:
Duck Duck Go auto-searches other sites when you do !keyword search. For example, !google duck duck go will Google us :)
1 - Restricting your (?) search to a site or group of sites
2 - Using another search engine
I'd suggest something along the lines of "You can focus your search with !word" (bold, not key)
I'd also suggest trying to make the listing more readable (or scannable - it's long ...). Perhaps an HTML Definition List ?