I think the chances of people doing an apartment 'swap' for their out of town/country vacation is pretty slim.
2 people going in the exact opposite direction and wanting to living in the other person's home. Seems slim chance to me unless those people knew each other in advance.
add - bluesmoon, learn something everyday. Though I think not all everybody wants to open their own apt for swap and instead would rather rent someone's for a week or 2.
It actually happens fairly often on couchsurfing. Couple A from New York wants to spend July in San Francisco and swaps with Couple B from San Francisco who wants to spend July in New York. I've seen it happen with entire families too.
Less likely to work internationally, but domestically, it happens. It's the key exchange that's the hard part, but the safest is to leave the key with a neighbour and then call them from the other side to give them the okay.
There are companies, like homeexchange, that have been in businesses for decades doing exactly that. Swapping, vacation rental, subletting have all been around far longer than sites like airbnb. Even craigslist has had a home swapping section for as long as I can remember.
Swapping homes is far more common than renting a room for a week. It's more common outside the US sites like gumtree, leboncoin, etc. have been doing this for years
This means people that go on vacation cannot take in renters.
(Sorry, your point was a bit lost in all the FUD that was in that article.)