[onewhitetree]

My humble (ha, I know) train of thought leads me to the simple point that Tolkien was a master storyteller, and a large part of great storytelling is romance. I think this offers a fairly tight solution to the query. Classic romance equation: beautiful, sought-after woman + heroic man who is unworthy in worldly matters = true love.

Now, who in Middle Earth is more beautiful than an Elf maiden? I think that the mortal men at question can also be considered more heroic than elves, considering their greatly shortened life spans and the increased susceptibility to the Dark Side (never underestimate the power). Additionally, men are certainly "unworthy" of taking Elven spouses, when materialistic concerns are taken into consideration.

Considering the emotions J.R.R. is known to have had regarding his wife, this particular version of the equation probably was close to his heart.