These names are not popular (how many do you know/visit on a casual basis ?) - A few, my personal experience doesn't show the value of an entire TLD or domain.
You don't really own them - In fact you do. You own the SLD
They are more expensive than real domains - You are talking like there are real and unreal domains. Yes they are more expensive than a .com domain but considering the chances to get a much better keyword it may worth spending a little more /year
They can go down (they have in the past) - I haven't heard about this, but yes, this risk exists.
You are the mercy of the company that owns the main domain - Substitute domain with TLD and it is the same thing basically.
f the primary domain is blacklisted, all the subdomains can be affected as well (just think of what would happen if one of your 'neighbors' doesn't behave) - Even an entire TLD can be blacklisted. Till now none of the domains us.com, uk.com, uk.net etc have been blacklisted. Don't compare co.cc with these.
We are talking here about services that exists for more than 10 years.
There are over 15 million links indexed in google for .uk.com (site:uk.com)