This article to me reeks as a prime example of the kind of journalism the Western press waits with bated breath to run in newspapers and online journals (ie "Russia is going to the dustbin not only economically but culturally", and/or "Putin is like Stalin").
If you read between the lines, it sounds as if they've polled only a younger set of the population, not representative of the older generation and definitely not a cross section of the entire population (that is the impression I get). Finally, the comments at article's end counter its initial premise. Chances are if you polled those same groups of the population in the UK or the US, the percentages would be, I am guessing, EVEN lower. In the US you'd have NBA football, baseball and Tee-bo taking first place, with probably a great percentage of the population not even knowing what ballet is. (Not being a UK citizen I can't speak for what's popular there).
In seeing the audience at the Mariinsky on a weekly basis, I can say that there is a section of the population that are devoted followers of the ballet (no doubt the same can be said of the opera here). They know, unlike most American attendees, what is what, who is who -- they're very finicky and usually quite critical. (I remember being shocked when I first moved here, seeing feats on stage that would have brought down the house in San Francisco and here got often no applause whatsoever). Based purely on my experience of living here for two years, I can say I dont agree with the article's main supposition.