I think the naming of Coins (is it an Altcoin, Bitcoin, or a Bitcoin derivative) is a tricky thing.
My gut reaction is to say:
1) Anything thing that forks with minority hashing power is an altcoin
2) Anything that forks with a majority of hash power is still bitcoin

But this creates problems because
1) What happens if the altcoin (minority hash power chain) later becomes the majority chain, do we relabel it.
2) This gives miners all the power to name what is Bitcoin, as users, businesses, exchanges (the majority) don't we get a say.

Because there are no pre-defined rules for any of this, only consensus, there is no escape from constantly fighting off hijack attempts by a vocal minority.