As far as the elves/eladrin thing, the best way to think of it is as the distinction between High/Grey elves and Wood/Wild elves, only made more explicit, and with Eladrin having this planar connection and heritage as Fey Lords. A lot of people who were complaining that 4e was "a P&P version of WoW" compared Eladrin to Blood Elves, which is really only apt insofar as they [i]are[/i] derived from that same character theme of "high-arcanist, tower-dwelling high elves".

The difference in environs, though, is mainly a planar one. Eladrin have a connection to the Feywild, the plane of faerie and life-energy, and the most powerful Eladrin still dwell there. If you wanted to plop Oberon or Titania into your game, they could easily be powerful Eladrin that dwell in the Feywild. On the material plane, your Galadriels and your Celeborns and your Elronds would all be examples of Eladrin-types (insofar as they all keep that otherworldly quality, and high magic nature), while Legolas would be a prime example of an Elf. Yes, Eladrin are more likely to be found near magic forests -that is to say, forests that are linked to the Feywild- but that itself isn't a major thematic difference between the two races.

I don't think they fleshed this out as well in the core books as they did in the preview materials, though; I think they're planning on saving a lot of it for their Manual of the Planes.