Is this really, some sort of idiomatic expression in French?
Is this not just a simple example of French requiring an article, where English does not. The word Years in For years requires the indefinite plural article des. Which can be translated to some, but is usually omitted in English. References Indefinite article (french.about.com) or Indefinite article (wikipedia)
I think that would produce a stressed word i.e. during 'some' years etc in which case it might sound better to uses quelques. There's a good discussion of it here: http://www.forum.french-linguistics.co.uk/forum/topics/when-to-use-quelques-vs-des?commentId=3179028%3AComment%3A73179
In English, they are both translated as "year" However, the word ending "-née" signifies a duration. Where it is not used, the word is a defined unit of time. You can remember this by the fact that when you add "-née", the word becomes longer when you say it. Without "-née" the word ends abruptly, it's clipped, and defined, just as the idea it represents is defined.
This link has some more detailed information: http://french.about.com/library/weekly/aa070100.htm
this is what i found, seems like the difference between "because" and "because of" in english.
My current understanding of this (and I am not an authority!) is that "pendant des années" would be used when talking about a duration of time in the past ("I lived there for years") and "pour des années" would be used when talking about a duration of time in the future ("I plan to live there for years"). I'm curious if I'm right about this, though.