Question on getting all site pages indexed in Google

I'm just kind of curious as to what some of the more experienced SEOers think about this.

I created 50 websites which all scrape Amazon for text descriptions only using my own php script (cURL is the greatest).. and each description is limited to 1000 characters. I've been grabbing very large category, high-competition keywords... such as video games, camcorders, tvs...etc.. just for the sake of getting exactly 10,000 results in my database.. which then equals 10,000 pages p/ site. I submit to Google sitemaps and analytics only.... just to get found and indexed within a couple days.

I have noticed that 3 of these 50 sites have all pages indexed.. and a couple actually have 14,000+ results (strangely). All other sites average between 15 - 30% of total records (pages) indexed.

When I google why all pages in my sites don't get indexed, I find site after site of how one should never expect that... that page rank, sitemaps, backlinks, etc all play into this. Well not here. None of the sites have PR or backlinks, they're all built in the same exact way and all at the same time (within a 2 week period). They're all approaching 5 months old.

Any idea why 3 of these sites would get everything indexed? Is there a chance that Google will fully index a site based on the category alone? (I'm going to test this by throwing up another site on the same category tomorrow). Is there any other reason someone might be able to think of that would have given these 3 sites so much better results with being indexed?