All depends on the specific product you're buying. For example, Best Buy's warranty has a feature called "no comparable product" (I'm not sure if its actually on the terms and conditions, but I used to work there and have done it a few times).
Basically, if they need to replace a product, they'll find something of like specs (in a computer, hdd, memory, proc, screen size typically). However if theres something that there isn't a comparable, then they give you the last sale price of that model.
I've done this on two occasions. Most recently, I bought a Sony SZ650 when it was end of life, back in 2008. Original price was 1700, EoL price was 1330. 13.3" screen, switchable graphics (before optimus was around), bluetooth, TPM module, fingerprint reader.
Fast forward to 2011, my laptop takes a dive and gets the screen cracked (no i did NOT do it on purpose, if anyone was thinking that). Brought it into BBY, sent it to service. They ended up issuing an exchange for it. Normally, with its specs (1.86ghz Core 2 Duo, 2gb ram, 120GB hdd), I'd probably get a 500 dollar whatever computer. However since I argued that I used many of the features that made it so unique, which is why I bought it in the first place, and they didn't have anything there that had even close specs, I got my original 1350 back in the form of a store credit.
I also did this for a monitor that went kablooey, as it had a bunch of different inputs (composite, component, hdmi, dvi, vga, svideo). I had originally bought it for 550 or so back in like 05. In 07-08 or so it died, no other monitors had that input type, so I got my 550 back and bought 2 22" monitors in its place.
I hear you on some things though, many times the warranty is too much of a % of the cost of the machine, or its something hta tdoesn't break often (or at least break with a high enough cost to repair it, eg. desktops).