When they are new, they work just fine. However, stock wires start to show their age in as little as 1 year (misfires, increased resistance). I had a stock set that went bad in about 18 months, and it took me forever to find the problem. Everytime I suspected the plug wires, I said to myself "they're only a year old, it can't be them". Sure enough...
By the way, when I say one year, I'm quoting David Vizard.
Lead Mechanical Engineer
Art Morrison Ent. Inc.