I was in contact with John Lewis a couple of months ago, trying to get a price match on a 504HDE.
After they had checked out the price match store details I had given them, I was told that the store that I wanted them to price match against wasn't open all day, so they wouldn't price match against them. Originally they told me it had to be a store which you could go into and look at the goods, as opposed to an internet only site without a store. You could go in to the store and look at the 504HDE.
I later contacted them with the details of another store which had long opening hours! The price wasn't quite as good as the first. I was then told that they wouldn't deliver 60 miles, even if I paid extra. They knew where I lived in the first instance, but didn't mention distance would be a problem.
I got the impression that they may price match, but up to a point. IMHO they weren't willing to price match to the tune of £700-£1000.
As for there 5 year guarantee, I'm sure some people may have found this useful, but, if you haven't already, have a look at the thread "Plasma Gas Charging Fault".
http://www.avforums.com/forums/showthread.php?s=&threadid=120995
There are members here who probably wouldn't recommend JL's 5 year guarantee at the moment.