I agree it sits oddly, but it's not between the 50D (which it effectively replaces) and the 7D, it's the 550D/600D (Not sure if the 600D has been released yet) and the 7D. The 7D has, to my mind, thrown a bit of a spanner into the heirarchy. I see it as something like this:
xxxxD - Absolute novice, stripped down version of the xxxD
xxxD - Standard entry point
xxD - Used to sit just below the 5D, as a "serious amateur" type upgrade for those not wanting/needing/being able to afford a pro body
5DII/7D - The 5D II is a seriously good camera, that's definitely "semi-pro" or "pro-backup" and I know a number of pros do just use 5Ds instead of the 1Ds. I see the 7D as the non-full-frame equivalent, that's faster and with better AF. Both do high quality video, although the 7D is newer and better on that front.
1D(s) - The pro-level bricks. The 1Ds being full-frame (but more studio-y than the 5DII in my mind, although I have zero justification), and the 1D IV is just machine-gun fast.
This is just how I see the range, mind.