Old thread, but i thought about these things when i was about to buy my I1 as well, but now i have understood that the differences between A/B/C/D are so small and non important so you don't have to care about which version you get, maybe that the A version legs are different in quality from the others, i don't know.
But the other versions are practically similar, the B and C versions can be fitted with the QR props anyway.
And about the different landing gear mechanism on the D model i have heard that it was changed because its cheaper for DJI to use that particular mechanism and that the quality is not better than the old ones.
Now if we are talking about the Inspire 1 V2.0 then we can start to talk about differences with the stronger motors etc, but not even that one has too many different functions. But that one is another story.