How does web2.0 pass link juice? I thought subdomain acts as a separate website?

How does web2.0 pass link juice? (I know they do)
For example; on wordpress.com

While the wordpress.com (domain PR is like 8)
username.wordpress.com (we start with N/A or PR0 - page PR)

Now.. on a second thought, in theory wise... I thought Google sub-domain acts as a separate website? So it shouldnt be passing any juice then? (or maybe bare minimum?)

Bare minimum. Basically they are like free websites. So people don't just link to their site, but they build a shit load of links to the web2.0s as they won't get sandboxed. So people will blast them with thousands of links.

I see.
So in theory, we are talking about "quantity" not "quality"

Not really. You want turn them into quality links.

best way i found was to create them massively and handle them manually, so they turn to become pretty valuable after 3-6 months

Do you guys just post casual blog style posts like a personal website or article type posts that are informative and what not?

Spun garbage all day long.