See Gamers initial Reaction to the DS announcement in 2004(They HATED it!! lol)

[MDMAlliance]

Soundwave said:

Once I saw Nintendogs at the E3 before the DS launch (2004) and Brain Training (which no one was talking about before launch) I knew exactly what Nintendo was going for and thought they could have some success.

Unfortunately for Nintendo that audience got sucked up by smartphones.

I think the DS appealed to both audiences and that's why it sold over 150m.  The casual audience by itself did not make up the entire thing.  Even without the casuals, the DS would have been a success.  Look at the game library and you'll see that.