Stealth providing powers were unable to be activated with other stealth providing powers which also provided additional benefits. For example, Cold Domination's Arctic Fog could not be activated with Stealth, so the player would need to decide what benefit was worth more in a given situation. Do they activate Arctic Fog for the +Def, +Res (Fire, Cold, Energy, Slow) or do they instead use Stealth +Def (All).
Now with these changes, players can have Arctic Fog active the same time as Stealth. And the power with the highest bonus in a given category is the active buff - so Arctic Fog provides some stealth to the player, but Stealth provides the most (outside of Superior Invisibility), so the active buff from Stealth will be was is used.
Edit: Furthermore, as Booper alluded to during the beta feedback thread, "SS is 35, IO is 30, Stealth is 55, while most enemies have a perception of 54' or less. So stealth by itself is enough, or the combination of the IO with basically any stealth power is enough." It was also mentioned that that is for the majority of the game's enemies perception distance - there are exceptions at higher levels and during specific content where using just Stealth may not be enough to completely slip past the enemy.