It's funny, I don't know why they say that either, however I've experienced poor performance from Bosch myself. I switched out a set of Bosch plugs AND wires with less than 10k miles on them for the factory plugs/wires because the truck was running like crap with Bosch.

However, my old '86 BMW LOVED those Bosch Platinum 4 plugs. Ran so much better with them. But they don't agree with the Toyotas too well, I guess.

'99 Tacoma Xtra cab V6 TRD
TRD Supercharged, URD 7th injector and 2.2" pulley, 32X11.5 BFG All-Terrains, OME 881 3-inch lift/Toytec AAL, 5100 Series Bilsteins all around, and ProComp 130 lights.
No I'm not some creepy naked guy...