If the route goes through the DF shops, then that's the way it is. I generally don't want anything to take with me - if I do, I've bought if before I've left the realm of free choice and it's in my checked bag - but occasionally on arrival at a destination I'll want a gift for my host, and if the price is right, I'll buy something.
Or electronics. I bought a camera in Heathrow last time through. I assumed it was cheaper than the shops outside the airport, and I needed a camera. And then spent a happy half hour in the lounge putting the thing together, losing the little wrist strap and then cheerfully stuffing all the packaging into a bin.
Sometimes they'll have fancy-schmancy travel gadgets that you don't get anywhere else and while I prefer to buy off the web, it's nice to be able to pick up and play with something before buying.
Places like Hong Kong and Singapore, the shopping can rival the lounges for entertainment. In fact, if there's a good bookstore with a cafe included, the lounge may not win out - some US airports have excellent bookstores. After a while all lounges look the same with the sugary snacks and the plastic coffee, but gimme a thoughtful book range with specials bins and fountain pens and notebooks and comfy chairs and barista coffee and I'm happy as. Buy me a postcard, sit down with a mugalatte, write a bullet-point bulletin and race it home.
Compass Books in SFO is a favorite: "Compass Books is a literary oasis in the midst of cattle car airport chaos," one reviewer notes. I was cheezed off because they weren't open before dawn on my last swing through. Peets Coffee was, and I bought a mug there, had them fill it with coffee and plonked it down on the counter when I showed the AC dragons my 30-day pass. Drinking out of it even as we speak.
But I digress. I'd prefer that the duty freeway be widened and re-routed for the keen "get me to the Flounge in the shortest time" traveller, but that's unlikely to happen so I don't get stressed over it. I largely ignore the advertising for cough I don't need, but I'm getting old and cranky and bald and ugly enough to smile at the fetching young staffers as i go by.