Mowers sold in the US just about all have a system to make it difficult for people to hurt themselves by putting toes or fingers into the blades when the engine is running. Except for Honda, they usually do this by having a bail on the handlebar that operates the engine's kill switch: if you aren't holding the bail against the handlebar, there is no ignition. Also, just to guard against somebody quickly pulling off the catcher and putting his/her fingers into the blades while the engine is still coasting down, there is a cutter brake that operates when you let go of the bail on the handlebar.
Honda's slightly different, and probably much more expensive, approach is to have the engine declutch itself from the blades when you let go of the bail, and the blades are stopped by a blade brake, but the engine keeps running. That way you don't have to restart it after you empty the catcher.
The bail cut-out is the reason those mowers have the starter cord handle attached to the handlebars, so you can hold the bail with one hand and pull the starter with the other.
Most mowers sold in Australia do not have the bail, so the engine keeps running when you let go of the handlbar and take the catcher off the mower. This is convenient for the user, but not especially safe.
