Main Motorcycle: '06 Speed Triple
Join Date: May 2010
Other Motorcycle: '96 Adventurer Cafe Racer
Extra Motorcycle: Not any more
I always assumed, at least here in the US, that it was sort of a spite thing. Basically the producers wanted to use a beverage in the scene and went to say Coke asking for them to cough up some money for the placement. If they didn't pay up, the producer would still use the can of Coke but would block it out.
Maybe Coke isn't a great example since that could easily be any number of drinks. But let's say you were shooting a scene that needed a certain style of motorcycle or car/truck/etc. You might not have a lot of choices to get the look you were going after, but the manufacturer might not want to pay up either. So you de-logo the vehicle.
Of course, I have no factual knowledge to base this on, it's just speculation based on my assumption of the greed in the industry and how blatant product placement has become.
'06 Speed Triple
'96 Adventurer Cafe Racer
and a bunch of other stuff
If everything seems under control, you're just not going fast enough - Mario Andretti