Why are you assuming all productivity increases are reducing labor needs? Look at your YC example: AirBnB's entire premise is to make use of capital that would otherwise go to waste (unused residential real estate). When you lower the cost of capital, you increase the value of complimentary labor. If nothing else, I'm sure it's boosted demand for the local housecleaners. Given how elastic vacationing is as a whole, the dollars saved by the travelers are almost certainly being shifted into other goods and services at the destination.