I like Elrod's response, and would like to include that component placement is done in a certain way to achieve certain results. I don' tthink you will be going to jail if you turn your speakers upside down. You likely also cut the labels off of your mattress and no one has knocked at your door yet. On the other hand you just might lose out on what the designer intended and you Paid Megabucks for to begin with. Why not just buy a speaker that was designed that way to begin with. At least they have taken design factors to mind when they created their design and it might just prevent you from throwing your cash out the rear window!
It is like the person that purchases a Lamborghini and then wants to put a Volkswagen engine in it. or at lest driving your brand new Lambo around in reverse all day long.
odd question about stand-mount speakers
Is there any reason you shouldn't turn stand-mount speakers upside down and listen to them that way, as long as you use some kind of vibration control/decoupler between the speakers and the surface they're placed on? The reason I ask is because, at least in a near-field setup, I would think having the mid/woofer ABOVE the tweeter would enhance image height/size -- assuming the tweeter is kept at ear level. (A couple of asides: I don't currently have bookshelf speakers, otherwise I would experiment. Will likely be buying some in the near future though. Also, I know that there are some stand-mount speakers that place the mid/woofer above the tweeter, but the vast majority do not -- most of the ones I'm interested in do not.)