speaker placement

Does elevating a floor standing speaker significantly reduce bass response? If so, 1) could the effect be reduced by inverting it and placing it close to the ceiling and 2) why do stands seem to be so popular? I see speakers both sold with stands and have dealt in my business with quite a few audio enthusiasts who request custom stands for their systems. 
All speakers get bass reinforcement from large flat surfaces like floors, walls, and ceilings. Speaker designers take this into account. Certainly all floor standing speakers are designed with the expectation they'll be on the floor getting the floor reinforcement.

But its not that simple. Its not just the floor. Its the walls and ceiling as well. So yes elevating speakers off the floor loses a little bass response. But this could be more than offset by moving them a little closer to the walls. Front or back, does not matter. In terms of bass response.

But wait, there's more. It does matter in terms of total frequency response and imaging. If elevating speakers moves the midrange and tweeters off-axis from the listening position that can be as bad as whatever it does to the bass. Or worse.

But wait, there's more! Stands affect more than frequency response. They also contribute (or detract!) from imaging depending on how well they control speaker vibrations. So yeah custom stands can make a big difference.

Putting it all together you could indeed flip them upside down and on the ceiling, but then you have to get them pointed correctly. Awful lotta work. For what?
Well.... audio enthusiasts seem to thrive splendidly on the very work you mention. I asked this question because my knowledge is limited and I had a customer request some very pricey custom stands. I didn't want him to spend a lot of money putting lipstick on a pig. Thanks very much for a clear and helpful answer. I will pass the information along.
You'd be surprised how much difference the right stand can make. A good stand will first of all put the speakers tweeter and midrange at just the right height and angle. It will be massive, and stiff, and highly damped. Tap or knock it, the sound should be sharp and die out instantly. It should also have few if any flat even surfaces that might reflect sound towards the listener. Finally of course it should look good.

Being custom they should also take into account whether the speakers will sit directly on them, or on cones or spikes. Otherwise all the careful measurements made based on speakers alone will be off by an inch or so when cones are added.