I'm not interested in discussing reading comprehension, so instead let's read what this person asked and anyone else reading this thread can decide what's being asked:
"i would like to know if i can get my ipad back through the device serial number? "
Practical answer is no, because apple won't help you. Notice the question above does not mention "locate"
Your second paragraph speculates about what apple could do based on certain actions. Instead of speculate, we know that apple is willing to completely wipe a device if connected to wifi, and/or lock it from use, based only on someone with a registered ID telling them to do so. The issue is, the device needs to be connected. These are fairly aggressive measures taken despite privacy and fraud concerns, and these measures really aren't that different from blocking activation.
The problem with apple's current security measures is a thief can wipe the OS and thereby remove the apple ID, rendering all of the measures useless. Theifs easily avoid the security messures.
A solution is to pull information from the device that can't be removed . . . like the serial number. I believe this is why people keep asking if apple will help them based on the serial number, because the serial number is extremely difficult to remove or replace. You could use any other device ID that remains the same after wiping the pad and setting it up as a new device.
As for your last paragraph, I agree, you don't "have to" register an iPad, but then again, you don't "have to" turn on find my iPad. For that matter, you don't "have to" create an apple ID.
I like focusing on solutions, so let imagine a world where users could, through the Pad itself, access a list of know stolen serial numbers . . . again, not that hard to do if apple wanted to do it. This alone might devalue stolen pads by reducing the market for them. If I plan on buying a used pad from a seller, I check the list of known stolen devices, and avoid the purchase. Better yet, I can report that the pad is being sold by someone . . . This may not stop the sale of all stolen pads, but it would certainly make it harder to sell a stolen pad, and thereby decrease the value of stolen pads, hopefully leading to fewer pads being stolen.
Other points from your last paragraph: being a licensed lawyer, I would point out that there is no "order" you can get from a court based on an offense report. I like your idea of requiring a police report to list a stolen pad serial number: that seems like a reasonable requirement to demonstrate actual theft of the device.
In all of your post, I think your last sentence hit the nail on the head: apple won't do these things "for their protection", which is another way to say they don't make money providing these services. I am simply challenging apple to figure out a way to make money BY providing the service people want.