Indeed, and also people buying second-hand are pretty unlikely to buy brand new if they aren't able to find the second-hand item (or use it). It's similar to piracy in that respect, that some people who pirate might have actually bought it, but the majority likely would not have anyway so can't just say "1,000 people pirated our thing, therefore we lost 1,000 sales". The cynic in me thinks they know that and just use it as a convenient way to over-inflate the damage piracy is doing to them, but that's a separate topic

On the other hand, lots of people buying audio gear new DO take the second-hand market into account, and will spend more on the initial purchase if they think the product will retain its value.