My LDS will ask for a card if you're getting an air fill and they don't know you yet. If you're getting a fill for paintballing or remote work with pneumatic tools, that's no problem at all. They don't ask for a card because they're scuba police. They ask for evidence of certification or experience for people's own good.
Think of it as a sanity filter for people who *don't* know better. Sure, you can learn to dive without formal certification, but that's not who it's designed to "catch". It's intended to catch the person who thinks, "You know, I think I want to scuba dive. It looks easy enough. I'll just buy me some gear and go do it." While I'm certain we'd all admire such a person's drive (and means, for that matter), but I for one really don't want them going off on their own (without even magazine articles or a good book) to start diving based on TV experience. Diving may not be nearly as deadly as some people would apparently claim, but ear injuries, DCS, and especially lung over expansion injuries (e.g. embolisms) *are* concerns for people who would dive without *any* instruction (even as little as a dreaded resort course, hehe).
Carding people is really about two things. The obvious one is the lawyers, but we should not discount the well-intentioned saw-it-on-TV people. We can dislike the lawyers all we want, but *asking* for evidence of certification or experience is hardly onerous. It's so easy to get a card these days (at least one agency, NAUI, even has an "Experienced Scuba Diver" option to provide non-carded experienced divers with a card with an absolute minimum of fuss -- I can do it in one confined water session and one two-dive boat ride if it comes down to that), and you don't even need your card with you now that there are cert lookups on the web sites. I think I can handle that for the ability to catch the unknowingly-unsafe divers-to-be.