Yes, the camera position is one difference. The other, as you mentioned, is that the X7500 comes with WM5, whereas the X7501 comes with WM6. However, as of August of 2007, HTC I believe released a WM6 ROM update for the X7500, and the filename for this is
RUU_Athena_HTC_WWE_2.21.405
From what I've been able to scour off the web, it doesn't appear as though there are any significant differences between the two from a performance standpoint.
FYI, this link has a quick description/review of the WM6 Rom features, Box.