In game description for skills while hovering over one shows a general damage or DPS number. This takes into consideration modifiers like increased spell/fire/physical damage, critical chance etc… which come from gear or passives. However, some other modifiers like those taken from the skill trees, like skill specific increases to crit chance or damage, do not show any effects at all.
In other words, the character sheet shows very detailed numbers for all modifiers FOR THE CHARACTER AS A WHOLE, whereas I request such information for each specific skill. Path of Exile actually does this really well, and shows much more detailed information for the 2 skills equipped to the mouse clicks.