I'm not sure anyone would notice a difference, especially with an interface like Siri where you can't easily flip enough coins to create a statistical distribution. And even then, pseudo-randomness would mean there's a seed, but that's probably shared with all other users (and likely not only for coin flipping), so I guess from your perspective there won't be a difference.
I don't know about iOS/Siri in particular, but Linux these days has good sources of entropy that can make for good randomness. And I'm not sure why you believe that Siri's random seed would be shared with anyone?
