Good on you for the apology, Greg, all too rare in the online world these days.....
The discussion has certainly raised some interesting points - I had assumed that Piko had gone over to plated wheels, didn't know that the new "shiny" treads are machined, but looking at a brand new Piko 4-wheel motor block sitting here on my desk (bought from Bertram Heyn at Llanfair, to power the centre-cab O&K MV9 diesel kit I got from him) it does indeed appear that the outer face of each wheel is coated with a matt black finish of some sort (presumably the powder coating as discussed), which has then been machined off the tread surface and the whole back face of the wheel.... not quite sure why the back of the wheel has been done, as there is no sign of any plunger-type wheelback pickup as per LGB. I assume that the Piko block has internal pickups running on the axles?
Oblique and off-topic question, though still relating to the Piko motor block - anyone know what kind of push-on connectors to use for the four terminal pins on said motor block? The LGB/Massoth type won't fit, because each pin is recessed into a semi-circular cutout in the top of the gearbox housing - and anyway the pins are very close together, so even if the usual push-ons would physically fit they would almost certainly end up touching each other (oo-er....).
If anyone has used one of these blocks on a DCC-equipped conversion or scratchbuild, I'd be keen to know what you have used.....
Jon.