When I compared two pictures of L.G.B Harz Steam Locomotives 2080D and 26801, I only noticed a few more rods on the 2nd wheel of newer 26801 and black steps detail than the older 2080D with simplified rod linkages and less detail.
Why is there a $400 difference between the L.G.B Harz Steam Locomotives 2080D and 26801?
Perhaps, 26801 is DCC ready, while the older 2080D requires an extra hour ($75 max) of time for DCC installation?
Same reason you can buy your gas for $2.79 a gallon or pay $3.19 a gallon at the same pump. Because they choose to charge that way. 
The old 2080D had a horrible sound system (by today’s standard), with a whistle and bell triggered by a long strip of plastic. If it had the sound at all, it think it may have been a 2080S, so disregard the above sentence. 
The new model is full of updated LGB electronics.
John Bouck said:John, thank you for sharing your experience with the sound in the 2080S, as I have seen them selling on eBay.
The old 2080D had a horrible sound system (by today's standard)...The new model is full of updated LGB electronics.
Does updated LGB electronics in 26801 include a DCC socket for connecting a decoder and perhaps LED lights rather than bulbs?
<<GB Steam Locomotive, German State Railroad of East Germany #99-6001 26801
Steam locomotive 99 6001 of the Harz narrow gauge railways in the livery of epoch V. Revised model with revised lights and reproduction of the corrugated plates on the running. Prototypical painting and lettering, multi-purpose outlet. Directional lighting. Length over buffers (16.14 inches) 41 cm.
Smoke, lights, DCC interface >>
Doesn’t have sound and doesn’t specify LED lighting.
Checking out the LGB 2006 catalog, I found this description of similar Harz model with more desirable features:
25802 - HSB Steam Loco, 99 6001-4, Sound
125th Anniversary Model. Watch for special ordering information.
A classic is reborn! The 99 6001 is a long-time LGB favorite, and this version is the first with the current livery and lettering of the Harzer Schmalspurbahnen. But it isn’t just a repaint: This version is made using new molds that offer more detail along with all the durability you expect from LGB. Look for the patterned running boards, new wheels and upgraded cab instruments. Then look at the operating features, like the onboard MTS decoder, digital sound, steam generator and directional lighting. But don’t just look: This unique model celebrating the 125th anniversary of EPL will only be produced in 2006!