Reading all these discussions, I wonder if "rules-light" and "rules-heavy" actually covers the points of the topic. To me, it seems more a point of a system of rules being very complex (aka "roll these dice, compare the result to the result in chart X, roll another die, add to result in chart X, compare to chart Y") vs. a pretty simple mechanic for task resolution (aka "roll this die, add and subtract the following modifiers, and compare to target number").
Then you can start talking about how detailed a rules system is, if it does cover all possible situations in the game with its resolution mechanic, and if it stays as simple or complex in that, or becomes more complex than the basic mechanic.
An additional point would be what is referred to here as "rules bloat", meaning the vast growth of additional, and sometimes redundant, rules that add layers of complexity or simply new modifier types to a basically simple game mechanic.
For myself, I'd refer to D&D 3E as a basically simple, pretty detailed, but far too big set of rules that tries to offer a solution for all possibilities, and suffers from a severe redundancy problem. For a more general approach, I'd pick RC D&D, which is a bit more complex concerning resolution mechanics, but which doesn't try to cover everything in detail.