I agree with you. I think that asking for gift cards is the same as asking for cash.
And I have all the same reactions, including the one that says, "there's nothing you could give me that I would want."
There is one instance in which I wouldn't be put off by it--when it's linked to a specific item someone wants.
Like: "I want to buy a sewing machine, so a gift card from Joanne's would help me."
or: "I love to knit, so yarn is always great, but it's hard to pick for someone else, so a gift card from Michaels would work."
Those are also the only ways I think are polite to ask for cash--even, and perhaps especially, when someone has said, "What could I get you for Christmas?"
We do an Elfster gift exchange w/ the cousins, and the organizer and I have contemplated making gift cards off-limits for that. It's the one present you have to buy for the holiday--put a little effort in.
I get that maybe they don't have any ideas yet (or maybe ever)--but then they should give categories, etc. Or just say, "I don't have any ideas, I'm sorry not to be helpful."
That said, I think that a person really should be able to say a few things when asked about gift ideas.
But I'll also say that I'm not in love with the direct question, "What would you like for Christmas?" I think the gift giver should put more thought into detective work, and I don't think it's good conversation to drop that inquiry into the basic back-and-forth.