Websites get hacked all the time. It's all too easy to use insecure code, to improperly secure your web server, leave holes in your PHP implementation, or whatever. It happens to governments, corporations, mom-and-pops, you name it. People have a habit of not giving enough thought to the security of their websites. However, when one of Google's highest profile properties gets hacked, it sends up a red flag or two.
Google is, after all, Google. They are the web in many ways and they sell advertising, applications, operating systems, and, perhaps most importantly, enterprise-class software as a service. When your corporation (or school, or SMB, or municipality) signs on for Google Apps, it's with the understanding that your data will be safe and secure. When hackers exploit what the BBC called "relatively simple attacks that allow hackers to place code into web pages," it undermines confidence in Google's services.
While it's true that this is YouTube and not Google Apps or a database of AdWords customers that was hacked, the fact that a Google property was so easily hacked remains somewhat concerning. How easy would it be to hack a publicly-facing Google Doc or Site? How about a publicly-shared Google Presentation? The answer is that it would, in fact, be pretty tough, but the perception of insecurity is far more important than the reality.
This isn't just about Justin Bieber or Google Apps either. YouTube is quickly becoming the platform of choice for much more than funny cat tricks. Video as a promotional, advertising, collaborative, educational, broadcast, and social platform is exploding and YouTube is right on the edge of actually making money. It's already making a fair amount of money for those with YouTube channels and now is not the time for it to look insecure to the networks, studios, and artists who will drive it to profitability (and to become the real cash cow it could be).
In Google's defense, they solved the Justin Bieber issue very quickly. However, they can't blow this off as "well it was just Justin Bieber." Google needs the Justin Biebers of the world, no matter how awful they are musically, because they bring serious traffic and serious advertising dollars. When studios are deciding between Hulu and YouTube for distribution of their material, there can't be any question about security.