B&W 800D vs 800 Diamond

Not in my experience - I have been listening to my 803Diamond the whole day - crystal clear open sound.
The trick is careful system setup. And careful component selection (not necessarily expensive gear, but good quality gear) because the Diamond series is very transparent to front-end performance - more so than the previous 80xD series.
I will add that the midrange (which is very good) does not reach standard of the diamond tweeter (absolutely exceptional) or the excellent rohacell woofers. In the previous 80xD I noticed some mild chestiness on the occasional male vocalist, but not on the latest Diamond series which surprised me (because I thought this was an artefact of the FST midrange, but it turned out to be, I guess, due to the previous woofer and/or crossover design).

The following reviews describe the differences:

http://hometheaterreview.com/bowers-wilkins-800-series-diamond-800-diamond-loudspeaker-reviewed/

http://www.stereophile.com/content/bampw-800-diamond-loudspeaker

http://www.audiovideo2day.eu/en/article/10402/Bowers-Wilkins-800-Series-Diamond

I wondered this also just before I purchased a used pair of 802D2 so I called B&W. BTW, these guys are so nice. They research things for you like how much did things retail for then. I asked them to compare like 6 speakers. The were Johnny-on-the-spot. 
Here is what they told me. They said the D stands for diamond in all of the models that have a number then a D. They may have come out with different models of 802D but they are all diamonds. The 802d that I purchased have a chrome ring on the tweeters. B&W were able to identify them as 802 Diamond 2

 

i hole this helps. If you are unconvinced just call them. They are wonderful people

* I hope

The thing I like the most about my past B&W and these are the midrange. Yes the tweeters are clear without being harsh. Yes those woofers are amazing for their size but still need a subwoofer. My friend has a 15” sub turned down low and it is amazing how it adds. 
The main thing is the midrange. If I play Chris Rhea or Robbie Robertson I can easily identify each instrument, even when they are all playing the same note. I find that sweet spot of stereo imaging is plus or minus 2.5 ft right or left. I can hear the vibrations of vocal cords, not talking about vibrado. If I listen to old music like The Stones or Rod Stewart then everything I just said can be ignored. Of course it stands to reason that in order to hear well with a good set of speaks one must start with a good source. I stream with a Cambridge. Even when songs play with 192 they do not sound as good as a CD at 44. There is a lot of variation in our hearing vs the frequency so what might sound good to one person may not sound good to another. Also, a hearing test will test a miniature set of frequencies, like 8 of them then plot a graph. My mid base area is not bad yet i like more mid base from my stereo so i tend to adjust for that in my equipment. It isn’t like the old days of just adding an equalizer. The point also is that a hearing test almost never gives you more than one frequency at a time so different people might perceive the separation of instruments differently. For me, if there is background noise I cannot hear someone speaking to me as well. This is common with aging. That is never tested for with a hearing test. U will just be told you are hearing less high frequencies. I do like that null test machine stuff. I think it is great for objectivity. I think rather than spend $750,000 on a set of speakers I would rather spend that money and get ear implants when they come out! Kidding of course