Ask HN: Why is Microsoft adCenter API not not available to all developers?

Thought I'd ask this here on the off chance there was someone from Microsoft or someone who uses the API around. Been planning on using this API for some time but only got stuck into research on it today.

Just wondering why something that is version 7 is still in some limited pilot program and not widely available? In looking around I've seen the same message from Microsoft, whether it be in blogs, on forums or direct email, that it will be released to all at some point but no date. These are from varying dates to, some over a year old sound like the same message as today.

What's the hold up on this thing or is it just a case of big advertisers being given priority while anyone without a track record of big adcenter spend being left behind?