Since Adobe bought Macromedia, they're going towards a web-based software approach, which exludes the massive size limitations of HD content.
Aside from their attitude towards HD (which I've heard is not good, at least for native MXF ingesting), Premiere is perfectly capable of editing HD with a fancy capture card from AJA or Blackmagic or a third party software solution like CineForm Aspect HD or Raylight.
