There are definitely the types that seem to think the streets are a racetrack and are very wreckless. I'm one of the 'other' types and I ride like a grandma and try to stick to open roads.
BTW, there are good reasons why motorcyclists don't always drive in the center of the lane. One main one is to position the bike so you are visible in the left mirror of a driver you are passing on the left, meaning you ride in the 'right track' of the lane. Another is oil and gas tend to be spilt in the center of the road, and most bikes don't have ABS. Riding in the left track will help prevent a driver passing you on the left from cutting their pass short into your braking zone. It all depends on the surroundings and riding defensively.
I'm a motorcyclist as well and I too tend to ride quite defensively. Another reason to avoid the centre of the lane is that the arrow markings tend to be slippery at times - especially on wet roads. The biggest factors, though, are the ones you mention - to be visible in the mirrors and to avoid fluids that have leaked from bigger vehicles - which usually is in the centre of the lane.
BTW, there are good reasons why motorcyclists don't always drive in the center of the lane. One main one is to position the bike so you are visible in the left mirror of a driver you are passing on the left, meaning you ride in the 'right track' of the lane. Another is oil and gas tend to be spilt in the center of the road, and most bikes don't have ABS. Riding in the left track will help prevent a driver passing you on the left from cutting their pass short into your braking zone. It all depends on the surroundings and riding defensively.