I agree that the 100m is by far the most popular in terms of 'celebrity', hence Bolt's fame (aided by his personality).
It is surprising to me that East Asians don't do better in the 800m. I would have thought that it requires the combination of 'nimbleness' and endurance (exemplified by Coe) that would make it perfect for East Asians. Coe, btw, was quater Indian.
East Asians might be able to produce world class but not elite sprinters, but still haven't produced anybody who seriously challenged for medals. China might eventually produce 100m champions if only by weight of numbers and wealth they might be able to throw at producing such champions (not to mention that they are diving head first into genetic engineering and eugenics).
The stats regarding white sprinters getting better and white middle-distance guys getting slower is misleading. First of all, whites never dominated sprinting in the 70s and 80s (although Wells should get credit for his gold medal). Nobody thinks that Wells was as good a sprinter as Ovett or Coe were as middle-distance runners. Christophe Lemaitre is an outlier indeed. Also, guys like Kilty are barely faster than Wells, and relatively speaking slower. For example, Wells PB for 100m was 10.11 and for 200m 20.21. Kilty's is (so far) is 10.01 and 20.34. When Wells was running those times, sea level sub 10 and 20 second times were almost non-existant, so he was in fact only a tenth of a second or so off the best marks in the world (before Carl Lewis came along). Kilty is much more than a tenth of a second off the very best in the world. Wells had victories over just about all the top Americans of the time save for Lewis. He even beat a pre-roided Ben Johnson. Kilty has never come close to beating the top Americans and Jamaicans and never will (at least over 100 or 200).
The reasons for British (and European and to an extent American) middle-distance decline are numerous. White sprinters didn't face a near sudden horde of African competition in the late 80s and 90s (many of them EPOd up).
Ethnic 'diversity' does matter. Imagine if China starts producing superhuman runners who sweep the board in every event thanks to eugentics and germline genetic enhancement? It's hard to see how it could be banned, as the athletes would never have needed to take any peds since birth - their genes would be responsible for their success. In any case, most people would think that athletics hadn't become 'stronger', it would have become weaker because only one country could effectively compete.