Another etymological note: the line «нечего, некому, не для кого» appears to be a Russian development — I cannot recall similar constructions even in other Slavic languages, while «ничего, никому, ни для кого» is pretty ancient and exists even in Lithuanian (where ни-=nie- etymologically and semantically, both from the reconstructed prototype *nei-).
Hi, I know the thread is very old but maybe it will help people who are looking for an clarification. Ничего/никого/никуда/никогда are "absolute" negative. And Нечево, некого, некуда, некогда stress absence. for example: Я никуда не хожу. I'm not going anywhere. (not going) Мне некуда пойти. I have nowhere to go. (absence - nowhere)