You've overlooked the most important thing: links are judged by many factors with the most critical ones being the strength of the page the link is on. If the page is off topic and/or poorly ranked whether it is on a subdomain, same domain, or external site really doesn't mean anything as a link from that page won't be worth anything significant. (Other factors include quantity of links of the page and anchor text of the links). So even if you spread your content around like that it won't matter if those pages are poor quality (SEO wise).
Having said that, Google doesn't see subdomains as anything different from subfolders so these links would be seen as residing on the same website.
I guess while I'm at it, don't underestimate the power of internal linking. If you have a large enough site and interlink your pages properly you can give yourself a nice SEO boost. It does wonders for Wikipedia. They do a perfect job of interlinking their internal pages with minor pages reaping the rewards of the links from other pages that have lots of incoming links, etc.