My guess would be that playing a piano in Equestria requires more skill (using the very tip of a hoof, for example). I have no idea how chords and arpeggios would work.
They could be several theories to explain this lets try a more obvious one: Another species, like diamond dogs for example, who are dissipated as being more ape-like (upright, opposable thumbs) recently created a large amount of this new technology which most likely was only first available to unicorns, who appear to be on the higher end of the class system as some pony explained above. This would explain how they appear to be designed for a completely differently formed species and unicorns having magic would have little insensitive to reverse engineer or modify the tools into something more suitable, however now may be in the process of doing so. Now this covers things such as the ovens and fridges but dosn't explain how non-unicorns have and use them, maybe unicorns are just bad at modifying them for non-unicorn use. Now onto a theory on the trains. Given that a spices like diamond dogs devolved various tech then traded it with ponies (most likely for gems found by unicorns) It may not be too far-fetched to assume that steam power exists, however may be limited the pulling ponies may have simply been transporting the engine unit to a station for refuelling, or minor repairs ect. Of course also noctice how skilled ponies are with their hooves. Now I'll have to fine comb to find examples but in one episode Mrs cake uses a rolling pin. Have fun explaining that.
