OWC will definitely replace faulty RAM free of charge (example: we bought 2-4 sticks for each of 6 computers a while back, and three of the sticks were bad - very simple return process and they sent out replacements before the originals were returned).

I think the OP's point is that buying RAM through Apple (at a hefty premium) is a significant convenience for some people: if there's an issue - any issue - with the computer, take it back to Apple and they'll sort it out. Buying third-party RAM isn't quite as convenient.

Of course, in my experience Apple will happily look at your computer even with third-party RAM, but they obviously won't fix any issues caused by it.