Typically I find that the 1/4 rule works as a good approximation - that is ifmy OG was 1.040 then I expect to get down towards 1.010... if I'm at 1.012 or 1.008 I don't really worry about it, but then I'm more relaxed about all that anyhow. Again, this is a guide for me, not a straight up hard and fast rule.
As to the wine below 1 and beer above, it is talked about elsewhere here, but basically wine has almost no non water and alcohol ... or it has it in a lesser degree then beer. So y ou have water at 1, alcohol at less than 1 and other stuff (tannins, malt proteins, hops bitters) that are generally above 1 bringing the average up. With beer at a lower ABV (generally) and with lots more residual protiens, it is almost always above 1.