re: unused blogs
There is no expiration date on blogs unused or otherwise. If you can make contact on your own with the owner of an unused blog then there is a means of a consenting blog owner to transfer the blog to another username account. http://en.support.wordpress.com/moving-a-blog/#transferring-your-blog-to-another-user-or-account
WordPress.com is a business that makes money from upgrades so fairness does not enter the picture here. Providing a free blog with outstanding free features as well as free hosting is what's on offer as well as upgrades and you can take that or leave it.