1) You don't have a warranty on Windows anyway, and you aren't risking your hardware here.
2) "Cleaning" means actually opening the laptop, pulling the heatsink, swapping out the thermal paste, and clearing out the dust. You only do this if the temps are actually tanking; otherwise, good paste can last years or even forever. Occasionally, temperatures spike because of a manufacturing defect, but that's rare. Dust buildup happens every three months for some people and never for others. Don't just open up your machine for no reason—watch your temps first.
If you do decide to go through with cleaning or repasting, I highly recommend this shop; I've brought plenty of my gear to them. They charge $50 and usually have it back to you in a day or two.
http://www.servislaptopa.com/Again, if it isn't overheating after 12 months, don't bother.
If someone tries to tell you they'll charge you just to blow out some dust: go to Best Buy, grab a can of compressed air, and do it yourself.
4/5) The retailer is legally liable for 2 years. If your laptop dies within that window, take it back to where you bought it (not to a repair shop!).
The cleaning thing has nothing to do with that. You're allowed to maintain your own laptop; the retailer or manufacturer doesn't get to dictate those terms of liability.
(They set the warranty, which is not the same thing as legal liability.)