Right now, Ovechkin is on pace for exactly 50 goals (14/23*82). His shooting % is also pretty mundane at 13.5. So 50 goals forecast is optimistic, but by no means outrageous. He had a lot of puck luck in the first few games, then had a fair share of bad luck lately, but it all has evened out.
Ovechkin is a volume shooter, in his last three Richard-winning campaigns, his shot totals were 386-395-398, and the shooting % hovered around 13. Last season, his low goals total was due to a wrist injury he played through, which brought down both his shots (to 313) and his shooting % (to 10.5). A similar thing also happened in 2010-11.
As of today, Ovechkin is on pace for roughly 370 shots for the season. If his shooting percentage stays at 13.5 (close to 13.4 for the full 14/15 season), he will get his 50 goals. If his shots end up at a lower number, say, 340, and his shooting % deteriorates to 12.3 career average (e.g., because Caps PP has been getting less efficient along with Ovechkin's PPG totals), he will end up with 42 goals.
So 45 seems to be a good over/under assuming OV does not miss more than 2-4 games (which has been a safe bet with him so far, but he is 32, so who knows).