Vienna had for several centuries been the imperial capital of the Austrian Hapsburgs. It was the capital of the Austro-Hungarian Empire, a sparawling polity the included modern Austria, Hungary, the former Yugoslavia, Slovakia, as well as parts of what is today, Poland, Ukraine, Romania, and Italy.

Vienna was a major center of German-speaking culture, as well as being a imperial capital with all the industry and institutuons that are implied with it. Until the 1920s, Vienna was bigger and more prosperous city than Berlin, and was rivaled only by St Petersburg and Paris in terms of population.

Today Vienna is only the capital of a small landlocked Austria, but in 1910, Vienna was the capital of one of the great powers of Europe, with a total population of around 45 million people -- more than France! Yet no one asks why Paris was a center of culture in the pre-war era!

This is a fascinating question, and one that I'm very interested in. No doubt there are many historical causes and I'll be curious if others can help identify them.

Pre-WWI Vienna is what sociologists of knowledge refer to as a "hot center." One factor of a hot center is that it starts to feed off of itself and perpetuate itself. Individuals are able to feed off that hot center and develop in ways that they would not if they had just happened to live in other cities at that time. These hot centers pop up in various places, only to move or die down. Vienna was one such manifestation, but of course certain larger conditions needed to be there in order to allow for a hot spot to form.

If you are interested I recommend "The Sociology of Philosophies: A Global Theory of Intellectual Change" by Randall Collins which includes a chapter on the Vienna circle. http://books.google.com/books/about/The_Sociology_of_Philosophies.html?id=2HS1DOZ35EgC