Geez, this thread moves fast. Another few comments from the picture.
First of all it is completely possible for the nose to travel straight but not the mains. In the automotive world it is called drifting. You purposely release grip on the rear tires by spinning them (in this scenario by rolling on grass and loose dirt). This frees up the tail section of the vehicle to react to side forces. This is achieved by yanking motion on the steering wheel. In this scenario it is created by a lot of factors. Such as engine failure, reverser deployed, "hitting the right wing tip on the ground" (although not seen clearly on the photo it was mentioned to happen) and inertia forces creat by whatever could have happpened.
3 seperate items from that foto corroborate the nose right side slip.
1. If the tail struck first in a nose right slip (meaning the plane moves in a direction more in line with the runway track while the nose points off to the right) it can be explained as a reason why the tail cone is resting further along the runway i.s.o. in line with the main gear tracks (more or less)
2. Try imagining the mains and nose gear to hit the ground one right after the other. (looking at the soil and deep tracks, together with a side slip hard landing, and it would have lost a lot of energy where it met the ground) You can then "place" the MD on the ground at the beginning of the 3 tracks. You will see that the angle the MD80 is pointing to is not the travelling direction of the main gears.
3. If the nose came down with a pronounced nose right slip, you can imagine the nose gear's initial contact would come offset. Looking at the part where people beleive is a burnt part of grass it can also be said that the nose gear chomped into the dirt and flung a lot of dirt towards it's initial track (thus to the left) the same direction the tail cone rolled off to.
I can totally envision this form the foto's and tracks. Please pardon my computer aided design
but this is what I envion...
the orange tail strike first and rolls in the initial track over the ground. However the drift (given in blue) is significant, when the nose plummets to the ground in the odd angle it spews dirt and/or hydraulics in the direction of travel (marked in red) this can also be seen where I beleive in fact the nose gear hits the ground. Due to the soft terrian and the slipping inpact, and the MD80 swerves around it's nose gear (drifting) for the few second it takes to reach the embankment.
Xander