Frankly I think they're just making stories up depending upon who you talk to on what day. If you are talking about .38 spl GDSB in a longer barrel handgun you MAY get the velocity up to what a .357 mag out of a 2" will be. Since the bullets are the same all you will have is something closer to the more powerful .357 mag in 135gr JHP SB load when shooting out of a 5 or 6 inch revolver. The .38 spl 135gr SB doesn't get a lot of expansion at the modest velocity it makes from a 2" snub anyway. As to extra penetration...well there's usually an inverse relationship between expanslion and penetration, so again it still sounds like a story.

The Speer SB 135gr in .357 mag runs about 130 fps faster than the .38 spl load.