Four a year not a classic rate of reading

Penguin really seems to be fixated on the idea that people who enjoy reading will only manage to get through four books a year. The publisher quotes research to that effect back in the summer on the re-launch of its classics range. An article on The Book Standard and a mention on the daily Bookseller blog reveal that the publisher and Amazon are starting a Penguin Classic Reading Group @ Amazon.com. The plan is to get through four books a year starting with Fifth Business by Robertson Davies.
It’s a great idea but why limit it to just four books a year. With the greater interaction that the web offers surely it would have been possible to get several groups going or at least a book a month?