Yes, that is what I'm seriously saying
"Are you seriously saying that you don't believe that a POS system should be able to have coupon validity information uploaded and do a basic check that the coupon is in fact valid[?]"
I am indeed so saying. If it were more cost-effective to do that than to bust people who commit major fraud, like the /b/tard idiot under discussion, and eat the low-level stuff as the cost of doing business -- which it is; keeping customers happy is a requirement of doing business -- then don't you think that's what they'd be doing?
Your dribbling excuse for a 'logical' argument does not follow; there's an obvious, overriding business need to keep track of inventory, and far less of one to keep track of every single coupon in existence, which would require a lot more new infrastructure than I think you're imagining.
How, for example, do you see the coupon database info being kept reliably up to date? If it isn't, you will certainly end up sooner or later with a situation where a coupon gets printed in some magazine with eight-figure readership, everybody cuts it out and brings it to the store, and then it gets rejected at the register because the store's coupon database is a couple of days behind and doesn't know about that coupon yet. Pissing off customers by screwing them over something that's no fault of their own is a great way to lose customers.
And even if you leave aside that scenario, why expect stores and manufacturers to implement a coupon-validation system that'll cost them more than they're losing to coupon fraud? That's just dumb.