Yes and no. Once the blockchain forks, the distinction between all those coins is very technical. Coins from one ledger cannot be spent on another ledger.

You're right though, cultural convention decides which blockchain is the "real" Bitcoin. Most people are using BTC at the moment, but Bitmain takes payment exclusively in BCH.

This might seem like a semantic quibble, but I think it's important. There will only ever be 21 million BTC, and only ever 21 million BCH. If Bitmain decided to charge 22 million BCH for their latest ASIC miner, nobody would ever be able to pay that bill regardless of how many forks there are.

For a blockchain fork to have any value whatsoever, people need to want to own it. Bitmain ASIC sales are driving demand for BCH. Every other Bitcoin fork is doing rather poorly.

Forks aren't diluting the value of BTC, because people know that BTC is the real asset. Everything else is like fool's gold.