It's also worth noting that Google's own regional websites DONT have pagerank 10, so I doubt they're doing any funny tinkering to skew stats.
Yahoo and google are two giants in this industry .So one does not care what the other company thinks about them.But there needs to be a standard convention about PR.
Add content to your website , get backlinks, add content , get backlinks, add content, get backlink etc... This is the only real way
Congrats to Yahoo, but I really don't think they are about Pagerank. It can mean nothing to them, they are a huge company. They know they have a lot of backlinks, traffic, and profit already.