I was in Nicaragua 10 years ago and had an absolutely phenomenal time without even a hint of danger. Honduras and El Salvador were sketchy, but Nicaragua felt fine. Must visits on the list would be: San Juan del Sur, and Isla Ometepe - in particular this hostel on that island:
http://fincamagdalena.com/
Best Coffee you'll ever have in your life. For sure.
Granada and Leon are really cool too. Managua is a hole, but all the capitals in Central America are kinda holes... except San Salvador, I really liked San Salvador for some reason.
Yeah, the advisory for Cambodia says the same thing "Exercise a high degree of caution" but no specific advisory. Be aware and you'll be fine.