[...] If enough people decide to update either of the above - rest of the network can decide to follow (this will result in soft fork) or not to follow (this will result in hard fork).
Soft forks / hard forks have nothing to do with whether the majority of the network is on board or not. It's a question of compatibility between the old and the new protocol rules.
A fork that is backwards-compatible is a soft fork, regardless of whether we're talking about 1% or 100% of nodes running the new software.
A fork that is not backwards-compatible is a hard fork, regardless of whether we're talking about 1% or 100% of nodes running the new software.
One practical difference lies in the likeliness of a chain split occuring. A soft fork is almost always safe, while a hard fork will almost always lead to a chain split -- unless 100% of nodes and miners are on board.
Good point that auto-update has been deliberately omitted as to allow nodes to decide on their own which version of the software to run. It's a very important design choice, giving people the right to "vote" on possible network upgrades.