My experiences have been similar to everyone else's.
I've had rods repaired or replaced for FREE (not even shipping and handling) from a manufacturer that I told on the phone I'd bought the rod second hand and that it had seen five years of hard use BEFORE I bought it, and I'd had it for three years. They sent me new rod, gratis. Wasn't a fly rod, though.
I think we have two separate things happening here. One is a dedication to customer service. Rod companies, if they aren't short sighted, recognize the benefit of customer loyalty and the stories that will bounce around sites like this one when they do something that basically costs them little or nothing. Many outdoor related companies tend to do this. See White Wolf's post about his vise, and numerous others posted here.
Another is the actual 'cost' to the manufacturer of a fly rod to do something like this. Last I heard, Sage charged something like $30 for a return/replace plus shipping. That's probably close to their out of pocket 'cost' (don't confuse cost with value here) for their high end rods. So it basically costs them nothing to offer this 'service'. Other makers have similar policies. Back when I was bass fishing, many rod makers had 'no fault/no question' warranties, but had a small fee, usually in the fifteen to twenty dollar range, for 'handling' the return/replace. I was told by several of these makers that this was the actual 'cost' of the materials involved.
So, they get great press, have happy customers, and it doesn't cost too much more than the labor/marketing costs which they would have paid anyway.
As far as 'enforcing' warranty rules, that's a no win for them in just about every case. Getting the 'dealers' to fill out the warranty cards would be nice, but last time I checked, rods aren't serialized and if the customer claims to be the original owner, how do you argue with them and still keep that valuable customer friendly reputation. It's just not worth it.
With the rising cost of rods, the warranties will probably get moe open, not more restrictive. Good for all of us in the long run because they are not going to lower rod costs anyway.
Good Luck!
Buddy
It Just Doesn't Matter....