When I was researching the purchase of my Panansonic TH42PX80, I went to Comet. The sales person also tried to sell me an expensive lead. He told me, would you believe, that if I used a cheap lead, the warranty would be invalid.
On the subject of warranties, personally I would only trust a retailer who gave me a five year warranty, with an item of this value, that is why I always buy from John Lewis.