is something different about this eames dcm?  

Errrr ummmmmmmmm uhhhhhhhh
The
back
is
upside
down.

It also looks tampered with.
You'd have to take more photos, or inspect it further yourself, but it looks like besides the upside down back it looks like it's been altered.
The shock mounts look like they have come loose, or have come disconnected and re-attached. The base and the seat look like two different generations. If you seat has the round medallion it should have a hollow base with nylon glides. Your base has either had the glides replaced, or is an earlier solid base. You can easily determine which generation base it is by the weight or by taking out one of the big screws under the seat to see if it's hollow tube or solid steel. I'd also look closely at those glides.

Hey Pegboard, was this an "option"?
The reason I ask is because I have a friend who bought a house designed by a regional modernist that came with 12 vintage DCMs (same feet as pictured) around a custom dining table that is actually suspended from the ceiling. The DCMs at the two heads of the table had the backrests turned in this same fashion. The vintage matches these posted here so was it something that HM did at that time or did someone take the liberty to do this themselves in both instances. How many times have you run across this yourself with all of the DCMs you have seen?

Not an option.
And I think it looks really weird.
Even worse on an LCW.

I have seen DCMs with the...
I have seen DCMs with the back upside down more times than I can count. I don't know why people do this, as the back is form fitted for the human body. It looks weird and feels weird.

is it possible they shipped with the back off....
leaving the end consumer or furniture retailer to put it on.
If you are not familiar with how it's suupposed to look, perhaps one's natural inclination was for a straighter looking or "winged" top to the back panel.
Just a guess.

DudeDah
Woody and whitespike are right. The chair was designed with the back in a single orientation. If you see it upside-down, someone has turned it around.
I've seen it many times as well. I'd guess that someone took the back off to clean or repair it and put it back together wrong. I've bought chairs with the backs on upside down, but I always scrutinize the shockmounts to make sure they are well attached (in case they came off and were re-glued).
I'm still curious about the base on this example. Those glides are most commonly seen on Evans production chairs, by the time Herman Miller began to produce the chairs, they'd switched to the rubber boot glide. You sometimes see chairs produced in the transitional period when they had more bases or seats left still to use (this is often the case with fiberglass armshells) so the change is not so cut and dry. However, an Evans-era base with later seat and back makes me wonder what's up with the chair.

They are everywhere!

this thread just made me...
this thread just made me discover something wonderful about my dcm pairs. they have solid metal base, their evans, whoopee.

Solid base
Not necessarily Evans.