Righteous rant, and absolutely right: there isn't really any excuse for a 2D game being slow these days. I suspect some of this is due to unpredictability of GPU performance; that's why the nvidia driver ships with 300Mb of compatibility shims.
A lot of modern games run slow because devs are using common 2D/3D engines which focus on cross-compatibility and ease of use over speed.
Testing in a lot of basic 2D engines also focuses on low performance, e.g. for an RPG where you'll have a dozen sprites moving around, instead of say 500 ships/weapon shots in a shmup.
