Call them modules, plugins, libraries, or widgets: any project that relies on an ecosystem of independent tools eventually hits the Platypus Problem: inexplicable, emergent complexity. That kind of complexity can confound the best software architects and community organizers.
The problem isn't insurmountable, though: by applying what we know of real-world ecology to Drupal, we can better understand the problem, gain insights into our own community, and identify important coping strategies. We can't eliminate complexity, but we can understand it, and knowing is half the battle.