planet.ubuntu.com is a great resource for the community, it is both an aggregation of some of the best blog posts in English about Ubuntu and also an aggregation of blog posts from Ubuntu Members. As the community of Ubuntu Members grows (currently 616 people and rising at an average rate of 10 per month) there will be a greater number of people who have English as their second or third natural language. If we continue to have English as the strongly preferred natural language then some people who are Ubuntu Members are going to not write content for the planet. It is my view that the important aspect of planet.ubuntu.com is that it is an aggregation of the blogs of the members, not that the posts are in English.
If someone wants to build and administer a planet with an objective of aggregating "great blogs about Ubuntu in English" then that would no doubt include some non-member blogs. Thus "great blogs about Ubuntu in English" is not the primary objective of planet.ubuntu.com
planet.ubuntu.com is a showcase for the Ubuntu community, I think it is great to prove that Ubuntu is built and backed by a diverse international and multilingual community.