The core devs may want to change the definition of a hard fork in order to make this claim, but it has. If it had never hard forked, you could still run the original client
It's debatable what you call bitcoin, the network can only be what it is if all people agree.
Back then everyone agreed on that, plus satoshi was still present, so I think those improvements were legitimate. Not to mention that bitcoin was worth almost nothing, so it was no big deal.
However with ETH at 1 billion market cap, we have to draw a line, and say that that is enough, and keep the status quo, otherwise powergrabbers will start implementing all sorts of "patches".
A hard fork with 10 billion $ worth of bitcoins is unthinkable.
https://www.reddit.com/r/Bitcoin/comments/4twge6/the_ethereum_hardfork_demonstrates_why_full_nodes/I myself will become a full node from now on, to show support for Bitcoin Core, join me!