the nature of spacetime and gravitation seem to have followed him to his death.

Certainly. But it was not the only idea he worked on, as I commented.

Perhaps I'm reading too much into it, but I interpret "Most of the great scientists worked on a single idea their entire life ..." as working on a single idea, to the exclusion of others.

Otherwise the statement would be "Most of the great scientists worked on an idea their entire life"

FWIW, using the list from http://listverse.com/2009/02/24/top-10-most-influential-scie... :

Marie Curie: received Nobel Prizes in Physics for her work in radiation and in Chemistry for her work in radium and polonium. If the idea here is "radiation" then Einstein's idea was "physics" and Darwin's was "biology"

Alan Turing: died entirely too young. Best known for early work in computers. Then switched to mathematical biology, specifically morphogenesis.

Niels Bohr: perhaps "nature of the atom" or "quantum mechanics"

Max Planck: Black-body radiation and special relativity

Charles Darwin: evolution (not really a small idea)

Leonardo da Vinci: not applicable

Galileo Galilei: astronomy (I can't think of a smaller "idea" for his body of work)

Nikola Tesla: umm, "electricity"?

Albert Einstein: see above

Isaac Newton: optics, gravitation, physics .. and then the Royal Mint, counterfeiting, and a whole lot of alchemy.

It's hard to conclude that these people worked on a single "idea", though some worked mostly in a single field.

Most of these people didn't even work in a single field... Tesla, Newton, Planck, Curie, Turing, Galileo...

Yes, I believe that is my point.

I may have not stated it well, i did not mean an idea to the exclusion of others but rather that they but that they didn't stop working on every single idea they took upon for a long long time. From the list you give, there arent any scientists who put their research on a subject "to bed" , unless it proved a failure.

Umm, Newton? The latter part of his life was research in alchemy and biblical chronology.

If you say that Newton "worked on a single idea [his] entire life", then what was the idea?

In any case, the observation is incomplete. All great scientists slept at least once a month doesn't mean that sleeping at least once a month is a distinctive attribute of great scientists.

If most great scientists work on a given topic all of their scientific career, is that not mostly because most scientists do the same?