+3/+3 skeleton/mastery are hard to get especially from shopping, the cost is too great to sit trying for them with a clvl 1 character anything over about clvl 8 and you will have less of a chance to get them. By using the chippy el/eld you force the ilvl to 1 which forces you into tier one of the staffmod tree which gives you a 90% chance to get a staffmod in the clvl 1 range instead of the clvl 6 range. so the skeleton/skeleton mastery are more easily found. It also guarentees that the wand will have the 2 sockets you need since you are socketing and controlling the values in game. It over all is safer to do it that way or wait for a white wand to drop with those staffmods, then to go back and forth shopping for them at a 10% chance to drop 2 tiers twice or 1% chance overall saying that you get 2 or more staffmods. The 90% sounds a lot better but with the extra work to find it they probably come out to the same amount of time spent searching but the make your own method gives you experience and other items while you work on it.
Malachi - Staffmods are the +1-3 specific skills added to an item. There is only one instance when you can get +skill tree with a white item and that is the amazon specific items. If you go to the specific items pages on purediablo.com or arreat summit you will find out about how the staffmods and other "auto mods" are applied and available. To figure out how they are applied takes a bit more work and searching through the forum/talking with RTB or Thrugg would also work. Basically when an item is manipulated it is allowed a chance to get staffmods and other "auto mods". This only occurs during a reroll (does not matter which type of reroll) and when the ilvl is changed (which is why the low quality to normal quality rerolls staffmods).
Each item class has a set of automods that can spawn with it. For example take the club it has a 100% chance to give "50% more damage to undead" that is an automod but the chance is 100%. another example is the staff it has a chance to get 50% more damage to undead, mana, +1-3 single sorc skill (3x). Other items have automods as well the amazon spear for example has the chance to get +1-3 javalin skill tree, I think its 3/6 for +1, 2/6 for +2, and 1/6 +3, but I am not sure about those numbers.
In short amazon specific items are an exceptin and are the only items that can get +skill tree as a "automod", that means all other items will not get +skills or +skill tree as a white item.
And no I am not going to test with low quality items just ones I find in game, I got out of the testing thing long ago and went legit so I would like to avoid it in the future, my chaos blade is the last nonlegit item I have.