I didn't differentiate between them, because - really - do you think the miners take a close look at the protocol the software they are using actually implements? Much less so the end users.
I see the software engineers of the Bitcoin clients as a largely underestimated force in the network dynamics. Even one subtly placed bug could bring down the whole currency in the long run.
The majority of miners would need to adopt the new software, and in theory the "economic majority" would too: https://en.bitcoin.it/wiki/Economic_majority