I have also seen people buying luggage, mostly smaller carry on bags - they look at their tired well travelled one and then at the tax free super modern one and just trade it up there and then. Like I said, I am pretty sure you can get lots of stuff delivered by the retailer, if you look around the airport there is lots of stuff much too large to carry on so has to be delivered.
...and at the end of the day, its all great advertising - you have hundreds of thousands of travellers, in a travel mindset, looking at your travel products - nothing to stop that working at an advertising level and putting brands top-of-mind when those travellers eventually upgrade their luggage.
Doesn't seem so daft the more you think about it!