I actually think the logo's purpose is somewhat deeper. One aspect that I believe is crucial to Darkcoin's survival (once source is released) is remaining competitive against a carefully branded clone that intentionally avoids any of the "Dark" baggage. If we were to go open source right now I believe we'd be wide open to being completely dominated by a "light"-branded clone with strong marketing. Look at how well Hirocoin did in mere weeks, and it doesn't even have Darksend. Selecting an accessible, mainstream logo that avoids any dark connotations and doing some major work on branding reduces the scope for this.