I think you're missing a rather important point =======> Feudalism did not fail in the HRE, it failed outside of it, in countries such as France. Mind you, forms of feudalism remained (tithes, lords ruling dominions, peasants performing chores blablablaaaaaah you know all that), but if with feudalism you mean the system where power is dissipated to a variety of lower echelons and subsequently the sovereign ends up the weaker link, then feudalism failed precisely in countries such as France and prevailed in constellations such as the HRE. The political - not the social - exponent of feudalism was precisely a hindrance to state formation while overcoming it was the first step to national sovereignity by the dynast.
Feudalism did not fail in the absolute sense of the word. It was because of feudalism nations could develop at all in a europe without an effective form of currency and economy following the fall of the western empire.
You could however say that feudalism proved to be insufficient in the 14th-century and onwards, since now developed monetary and banking system allowed princes and kings to become less dependant of their vassals.
The HRE went through the same development in this sense that, for example, France and England did. However - the concentration of power came to effect the dukes (who became less dependant of their own vassals, and because of this growing independance distanced themselfs from the Emperor and fragmented the already unstable Empire) rather than the Emperor.
I would like to say that feudalism did not fail. Rather - I like to think that it evolved into something new.
But the question remains - Why did the HRE "fragment" (Or whichever word you'd like to describe it

) whilst other countries did not?
I think it becomes more clear if you don't regard the Holy Roman Empire as a German Nation at all. In fact - it was only called the
Holy Roman Empire of the German Nation after 1512. Rather - think of it as a conglomerate of ancient tribal groups which later developed into dukedoms that had no traditional bonds between them before the conquest of Charlemagne and the formation of West Francia.
I think this helps to explain the events in the HRE. Feudalism did not fail in the HRE, if you regard each duchy as a nation in itself "Germany" followed the exact same pattern as her western neighbours. It is a plausible theory, no?
Cheers!
- Desikratis