No need to be an asshole. The $15 a month accidental damage plan for cell phones absolutely does cover water damage--from spills. It does not cover full submersion. However, because it's pretty much impossible to tell the difference between full submersion and simple spill damage without disassembling the phone and analyzing it (something we never had the time or ability to do efficiently), we never denied anyone on this basis at my store.
As far as "returning" the device, it sounds like you have a different idea/expectation of what the service is. The Geek Squad Protection for mobile phones entitles you to a replacement refurbished phone. For laptops, it covers repair. It's advertised this way, so it's not like Best Buy is being dubious about it. If the device has been repaired twice (it used to be three times, but was reduced to two last year) for defects, on the third time, the "no lemon" clause kicks in and you are eligible for a replacement. This doesn't apply for accidental damage claims, where Best Buy will repair an unlimited amount of times unless the costs of repair exceed the value of the unit, in which case the unit goes "junkout" and the customer gets a replacement.
Computer models come and go so it's unlikely we would have the same model in the store if we were to replace the computer. For most customers (i.e. normal end user consumers who don't really understand computers), getting a new computer is an extremely complicated situation due to transferring data, configuration, reinstalling programs, etc. This isn't an easy situation to handle because of customers relying on bundled OEM software that isn't available on or differs on the new computer, the impossibility of transferring installed programs, they expect Best Buy to do all that for them, people have to dig through closets to find serial numbers, when they can't find them they expect Best Buy to just give them a new copy of Office, then they want Best Buy to replace incompatible accessories (spare batteries or AC adapters, etc.) etc. not to mention customers who do in-home services wanting us to come back out to their house for free to set things up again with a brand new machine, etc. It's a support nightmare whenever we replace a computer--it's usually much less headaches and frustration for all parties involved to just swap the bad motherboard and be done with it.