Yeah that's right. No routers needed.

All local wireless gameplay on the DS is the same ad-hoc networking, too. Some games, like Mario kart, could use ds download play which is the same thing but a host would send over full game data before playing, too.

The 3ds also used it for local streetpass.

Nintendo experimented with it a bunch, honestly, although I always felt it was relatively unexploited in the ways they did. DS download was cool though because it was a mobile console's split-screen gameplay, instead of selling you 4 games to let 4 people play.