Isn't it like this in many places in Europe now? Barcelona does 60 days and Greece does 90 that I know, as well. Maybe I'm mistaken on Barcelona.
If it's over 50% or you are not living there at all, you need a permit.
http://www.haniotika-nea.gr/90-meres-to-chrono-i-enikiasi-me...
It's 90 days, 60 days on small islands and you can only go over that limit if you're low-income. Compliance is a different issue, because Greece, but hopefully AirBnB and the other platforms will help police this.