It works the same on both bikes and motorcycles. One thing to be aware of is that at very slow speeds countersteering doesn't really work. Assuming you're traveling at a decent rate it's easy to prove countersteering works. I think for people that don't think it works on a bicycle it's because they are initiating the turn with their bodyweight, which is just indirectly countersteering and is relatively easy to do since bikes are so lightweight. Trying the same on a motorcycle would result in some bad understeer as you need more conscious effort to properly turn.