There is NO difference between a 3D blu-ray and a regular one except the 3D version of the film. Whether or not you can play them in a regular player depends on how the disc was mastered. Some have the 3D film on a separate disc - that disc will typically not play in a non 3D capable player, but they include a standard BD that will. Other discs may have both versions on one disc and it allows you to choose 2D or 3D (or will simply detect if you don't have a 3D capable player and play the 2D automatically).
3D conversion is NOWHERE near the same thing as watching a movie mastered in 3D. It is like using ProLogic to simulate surround from something that wasn't surround encoded: it sort of works, but not really.
