MicroCash will have an alternate 51% mining protection mechanism which will mean the power of the network is more in the users hands
Accounts store public keys so that once set it's more secure than ripemd160
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Sounds like they are storing the public key with the accounts so that it is "Set" once and can't be changed. This way it won't be relying upon a potentially weak hash to secure a public key anymore, but the actual public key. Probably also why they can reduce transaction size so drastically.