I don't know the answer to this question, but the city really seems to have the luxury vacation rental market cornered. Seriously — try googling "Barcelona," "apartment," and/or "luxury" and the results are crazy! I once found myself in Barcelona when nearly every hostel and hotel room was booked, and I randomly ended up in an incredibly beautiful 2-bedroom condo on Passeig de Grácia. The experience only reinforced my sense that the city is packed with gorgeous apartments.
Surfing the web, it's easy to find some theories about Barcelona's abundance of high-quality living and design:
The New York Times says, "Conventional thinking holds that Barcelona is Spain's gateway to European culture. Insofar as culture means innovative architecture and modern art, smart urban planning that prizes pedestrian-friendly boulevards...such thinking is right on the money."
About.com says of Barcelona's architecture in general, "Modernisme is slightly different [from Modernism] and is uniquely Catalan, which means that what you see here in the capital of Catalonia is something you won't find anywhere else."
Monocle Magazine has included Barcelona on its 25 most livable cities list multiple times and chalks it up to "intercontinental connectivity and near faultless urban planning" and says, "Instead of pandering to tourists, the city is putting residents first."
So, if you're interested in Barcelona's buildings and agree that it has some pretty stunning spaces, click through the following links for more photos:
• Art Nouveau Meets Mod in Barcelona
• Barcelona Apartments from Habitat
• Apartment Eye Candy from Destination BCN
• Budget Decorating Ideas from a Barcelona Apartment
• Modern Rustic Apartment In Barcelona
• Rough and Smooth Renovation in Barcelona
• Cecilia & Roope's Hilltop Home
Photos: El Palauet (1-2), Habitat (3, 4, 7), Destination BCN (5-6, 8-9), Lluis Folch and Jose Hevia for Arquitectura-G, via MocoLoco (10)