Just because an idea has been implemented into another app doesn't mean its bad.... if someone suggests it THAT means it is a good idea... See this is why things are open source so ideas CAN be SHARED. Not so that they can be shunned because you think your application is better with out it. Sometimes too many things is a bad thing but some ideas are just being outcasted because you think using other implementations are the devils works... The Powder Toy is just using Powder Toy's ideas... this is not Powder Toy this is The Powder Toy. Things are open source so you can use their ideas.
@Gamewizard71 Uberness is right... For example: Movable Solids is considered one of the best ideas, by most powderers, but it causes too many glitches and is very hard to code.
Simon actually implements most of the ideas that get suggested, but many of them don't work well enough in the game or do enough of significance to warrant being in the game. Open source doesn't mean dogpile code, it means the source is out there for anyone to see.
If you want a bloated piece of software that can't run on any computer known to man due to the lag, crashes, bugs, and otherwise pointless mechanics that don't work, then feel free to do it on your own schedule.