Since I'm still relatively new to the world of piano construction, take these thoughts with a grain of salt;
I have considerably more experience as a guitar player than a pianist, and I know that a lot of cheaper guitars are made with mahogany. Some just use it for the back & sides, with a spruce top, but others I've seen are all mahogany.
I'm a drummer by trade, and I've seen mahogany drums. In fact, my Yamaha kit that I gig with has some mahogany in the shells.
It is true, that with its tight grain pattern, mahogany is very durable and also very strong.
But in both guitars and drums, mahogany makes a thinner sound, with more emphasis in the mid range frequencies than the highs or lows.
I guess it all depends on how the wood is used. My guitar that I bought as as beginner instrument is made of mahogany, and it's painted black. It sounds great for a cheap guitar, but it can't compare to my new baby made of solid spruce and rosewood. On the other hand, my drums which are made with mahogany sandwiched between several layers of birch sound stunning.
But with any wood, certain types have certain characteristics. That's probably why you'll find poplar in inexpensive furniture, but not on quality musical instruments. Some people may prefer the sound of a mahogany soundboard. I've never seen one, so I wouldn't know.