I would say this is a good idea. But good luck getting anyone in a retail store to actually give you that in writing. Plus once they do, there's nothing saying that they will honor it..
when we say in writing, we don't mean to have the 16 yr old kid literally write out the "warranty" on a piece of paper. Best Buy should have pre-printed pamphlets or actual printed documentation with all of the information about the warranty.
It is required by law that they be able to provide you with the written terms. Always get this pamphlet/document/whatever - it is your only real protection.
If they promise you it - ask them to point out what page it's on. Carefully read the exemptions. Keep it around because and don't be surprised if you have to use it to get what was promised to you
Sidestory - I actually had a power surge that fried my TV a ways back. I called the warranty program I bought that covered power surges. They said they didn't cover it. I said
"I will read to you the contract that I have. The title is this and I am reading from page 23 if you want to follow along."
Person on phone: "But there are exceptions"
Me: "You are correct. Those are listed on page 42. Can you please point out the exact one that voids this claim?"
Rinsed and repeated through various managers. It took some time but I finally got the replacement.
Anyway - back to the true point: Consider this a pointed reminder that getting something in writing is what will protect you NOT 'he said, she said'
Always always (always) get important claims in writing. Read AND understand your contract!!!