Under my interpretation, both are "sorcerers" in a broad sense, for both tap into the same universal power source. The difference is that magic-users bend that power to their wills, which is why they acquire spells faster and their magicks are generally destructive and self-aggrandizing. Clerics, on the other hand, bend themselves to match the warp and weft of the universe's power; they improve themselves in accordance with its laws.
This solves a lot of the mysteries of D&D magic in any edition. How can both sides in an internal religious dispute still have magical powers if at least one of them must be considered heretical? Why doesn't worshiping a more powerful god give you more powerful abilities? How can clerics worshiping demons get the same powers as those who worship true gods? What about clerics who are worshiping beings that claim to be gods, but really aren't, like in the module Against the Cult of the Reptile God?
It also explains the high-level spell acquisition of paladins and rangers. Both classes come to the same harmony with the powers that underpin the universe, but in a very round-about way. Finally, rangers don't have to choose a divine patron when they reach a high enough level to start casting spells. The spells don't come from gaining the attention of the gods, but rather from an inner discipline that slowly brings the ranger into line with natural flows of energy in the universe.
But you can take this idea even further. How is the high-level fighter able to take on entire armies of foes and emerge victorious? How can the high-level thief pick the pocket of even a wary individual? Could it be that they also achieve the same sort of harmony with the same natural energies, albeit in a rather limited way? This would make Earthdawn and D&D far more similar in their metaphysical underpinnings.
It's a neat idea, and certainly worth further consideration. As for me, I'm going to continue tinkering with my sacrificial mechanics. After all, one of the joys of early editions of D&D is how amenable they are to being bent around the themes and tropes of individual campaigns.