When we speak of "the Woodstock generation" are we talking of all the people that were born between two dates, or are we talking about all the people who had some common experiences in the 60s?
When we speak of "a new generation of antibiotics" are we speaking about the antibiotics than came up after a certain date, or about a class of antibiotics that have some new features in common?
I frankly don't think it's strange that the issue comes up again and again. Different definitions for console generations are constantly mixed up by developers, analysts, PR guys, journalists... basically by anyone in the industry.
And yet, some people on this site are adamant in saying that the only acceptable definition is chronological, because of the one true source of Wikipedia.