Premiere is an editing suite. After Effects is not an editing suite, rather a compositor and motion design suite. I can understand if the distinction is lost on people who have never used the latter, but trust me, it is not lost on motion graphic designers.

You might be surprised to learn that even Apple sells separate editor and compositor software: The just-released Final Cut Pro X is a separate product from Apple Motion.

I do agree, though, that Adobe should consider merging apps when appropriate.