According to Lovefilm, “We’ve been asked to make this change by the Studios who provide us with the films in the first place, because they’re insisting – understandably – that we use robust security to protect their films from piracy, and they see the Silverlight software as more secure than Flash.”
This might just result in quality improvement for Lovefilm’s streams, since Silverlight holds a technology known as Smooth Streaming that will automatically adjust the quality of the video stream to the best level, depending on the quality of your Internet connection. This means that buffering is reduced in the long run for those on a low broadband speed.