I read only today your post. My analysis of the race of Rodgers is very simple : he, like Robert Cheruiyot, were destroyed by the weather, too much different from that in Italy, where they trained. The shape of Rodgers was really very good, but his training after Lisbon was always in a temperature of 6/8 degrees, many times with snow and rain. The same happened to Cheruiyot : I had some info from his coaches that he did very important workouts, expecially in long run. So, when they arrived to Boston, the temperature was OK, but during the last 3 days grew up till 30 degrees, with very high humidity.
Rodgers made some mistake, not drinking during some refreshment. This is a big mistake from a top athlete, and can also explain because in the past he won Boston and NY when temperature was very low, and lost when was hot. I didn't know this problem before, as when I followed him in training he drank only a little, due to the cold.
So, I want to say exactly my thought about HM and marathon.
When an athlete is able to improve his personal best in HM, already good because he ran many HM in his life, and is a HM runner (before moving to marathon), this happens because he works too much for speed and not enough for long run at fast pace. Normally, this is a mistake. For example, if Paul Tergat, able runningin 59:17 some year ago, preparing marathon can run the world HM record, I think that his preparation id not complete for a full marathon, or that he is able to run in 2:02 if his preparation regarding long run is very good. But in any case he must be ble running a little under 1 hour for running his marathon very fast, not of sure in 61:00, that in this case can demonstate a lack of training regarding specific speed endurance.
In the case of Rodgers, he ran only one HM per year, and never reached his real potential. So, he was able to improve his PB not because of his training was with too much speed, but because BEFORE never ran at his top level.
The same I think happened for Lel and Cheruiyot. The problem of the "Italian Kenyans" (coached by myself or by Rosa, nothing changes) was the difference of weather, that for example runners in London didn't find. In Turin, the day before, Frederick Cherono (training last 4 weeks in Italy) ran very easy in 2:08:38, and really he was very much weaker than Rodgers, that in any case is not talented for running in hot conditions.