On an engine I've just built for a bike, yeah, I change the oil right away. I also use conventional oil for break-in, and I wouldn't run it for any length of time anyway. I also drop the oil pan and clean the screen on the oil pick up on a bike engine, but I don't on a car because getting the oil pan off a car is not a simple task, even if you appear to have full access to it from below. The FIPG they use to seal the oil pan is no fun to split.
Added to this, you get your car from Toyco with oil in it. It's already been driven by who knows whom a few times. It was also assembled in a climate controlled environment, maybe not a class 100 clean room but certainly class 1000. There isn't going to be much in the oil pan or the screen. Doing it at home is a lot different.
AFA bikes, it seems Kawasaki throws a handful of crap in their engines. I don't know why, but we always called it the Kawasaki swarth. Brand new, straight from the factory, crap in the oil pan every single time on first tear down. Yamaha, Suzuki, and Honda don't have this issue.
The other big deal about bikes is they almost all have wet clutches. Debris from the clutch friction material is one of the biggest pollutants in the oil on all bikes, and because the oil runs through a constant mesh gearbox and wet clutch, it is infinitely more abused than any car engine.
Last but not least, if you are doing frequent short drives (less than 10 minutes operating time) you need to change your oil much more frequently, and yes, 3000 miles would not be a bad choice if you are using conventional oil, and I would venture to say even I wouldn't run more than 5k on synthetic if I did a lot of less than 5 mile trips.
The key is this: water condenses inside the engine when you start it up. It's a simple fact of adding heat to the air. The water condenses on the sides of the block and runs down on top of the oil. On its way, it washes off byproducts of combustion, including highly corrosive acids from impurities in the fuel (like sulfur). Because the oil is cold, the water sits on top and sloshes around, but doesn't enter the oiling system.
Once the engine gets up to operating temperature, the oil sump will be somewhere between 180F and 200F, possibly more depending on conditions, but ideal oil temperature is 180F. This is enough to cause the water on top of the oil to vaporize, purge the oil of the impurities the water carried, and get pulled through the engine's PCV system, burned in the combustion chamber and run through the catalytic converters to clean up the bad stuff.
If the engine doesn't get hot and the water doesn't vaporize, it sits on top of the oil waiting for the next cold cycle to add more water and contaminants to the oil and eventually form sludge out of perfectly good oil. This is why more frequent oil changes are necessary for people who typically make short trips. It's actually better for the engine to run for at least 20 minutes every time you start the engine. It just doesn't make sense all the time for other reasons.