You got that right
My IWD party (the 4 survivors from the Belhifet battle) finished the game in 5 days (mostly because they were all multiclassed fighters), and I was like: that's it??
But if you played the game from the start of IWD then pop off into HoW when you reach Kuldahar, it makes IWD real nice to play, cos your characters would be that much stronger after defeating Icasaracht and that would make the tedious hacking in the Vale of Shadows that much easier.
Maybe that was what they meant by "expansion", huh?