I thought this was a moot point, settled and done, but a recent errata opens up the question for me again.
Vision and Light (p. 183). A heavily obscured area doesn’t blind you, but you are effectively blinded when you try to see something obscured by it.
This corrects the following rule:
A heavily obscured area–such as darkness, opaque fog, or dense foliage–blocks vision entirely. A creature effectively suffers from the blinded condition (see appendix PH-A) when trying to see something in that area.
Now, this errata implies to me that being within a heavily obscured area does not prevent one from seeing OUT of the area, merely from seeing INTO the area. For instance, a rogue in an area of deep shadow would be heavily obscured to the guard standing by the streetlamp, but the rogue could easily see the guard. (Substitute thick foliage and elf for a less light based situation.)
On the other hand, the rogue would be effectively blinded to anything else in the same area of darkness.
So, what in the Darkness spell specifically prevents one from seeing OUT? The only indication I can see is that "A creature with darkvision can't see THROUGH" it and that doesn't really convince me. Can Darkness be interpreted as simply a mobile, impenetrable shadow?