Sorry for being so uninformed but what happens if there is an error in the logic? Doesn't that mean that it's not possible to update the smart contract?
There have already been multiple incidents involving bugs in "smart contract" code being exploited to steal funds, one within the past few days[1]. A particularly nasty case involved something called "the DAO", which was an attempt to do something like a distributed VC fund, but had a bug which allowed any participant to steal all funds contributed. That one got backed out by a hard fork of the Ethereum blockchain, but that's obviously not a stable or scalable solution to dealing with these types of situations going forward.
Basically yes, and this is reasonable from a security perspective, otherwise every smart contract would basically have a trusted administrator.
But in many cases you do want some ability to upgrade the code, and then you simply program in that ability by creating a repointable proxy with whatever authorization logic you want.
Yes the block chain is by definition immutable. So no means to update the contract the only way if it is a ENORMOUS mistake would be to fork it: read about DAO hack FYI
