OK, I've found it. But they didn't clarify what skill is in which group at that time:
FoF: February 15, 2008
"When I'm crafting an item with a runic tool, do all properties have an equal chance of being used??"
Not necessarily - some properties are more common than others, and it depends on the type of item. Here's a general overview of the weighting:
* Shields and wands - all properties have an equal chance to be rolled
* Fishing poles - Spell Channelling is twice as common as everything else; all others are equal
* Jewelry - All properties are equal, with two exceptions: Night Sight is quite rare, and skill bonuses are grouped - see the note below.
* Talismans: Slayer, Crating bonus, crafting exceptional bonus, and creature resists are all weighted equally - all others are substantially more rare.
* Melee weapons - DI is quite common, HLA is uncommon, Hit Area is quite rare - all others are equal
* Missile weapons - Same as melee, except DCI is quite rare as well.
* Armor (non-elf) - Night Sight is uncommon and hp regen and stamina regen are rare; all others are equal
* Elf armor - as above, except night sight isn’t even an option
Property "groups": Certain types of properties are rolled as a group - slayers and creature resists on talismans are rolled for as a property, and then the sub-type is rolled. All the references to them above refer to the chances of these types being rolled as a group - any specific element of the group will of course be much more rare. This also means that you can't get, say, more than one slayer type on a particular item.
Elemental resists are slightly different - the math works out such that rolling any resist is the same chance as rolling another of the "regular" properties, but they are actually treated as five separate properties - so you can roll bonuses to more than one resist on a single item.
Skill bonuses on jewelry are a little bit different - the available skills are divided up into five groups of five or six skills apiece and then the subtype is rolled. It's possible to get more than one skill bonus, because they actually are treated like five different properties.