Wordpress.com has 502,000 backlinks showing in Google for God's sake. That has to rub off on the sub-domains just a little bit.
Wordpress = easy regarding seo, but dont forget competition and your own efforts will decide difficulty too. Wordpress posts are indexed very quickly. I recommend all in one seo plugin, and sitemaps plugin for obvious reasons.
Maybe it is yes. It is all depends on the person actually. If you do it right, they you deserve what you did. honestly, wordpress is really machine to be used. you should try it
I'm not sure about immune to sandbox trapping - maybe if hosted on wordpress again due to the trust of the wordpress domain as a whole. Definitely not convinced by "There's solid evidence showing that Google is, somehow, biased towards website that's created in WordPress's blog styles." I don't understand what you mean by this? If you have a good heirachical site structure that is interlinked well it doesn't matter on the site/blog style
There are strong evidences to show that google is definitely favoring the blogs hosted on wordpress and the irony is that it likes the wordpress more than blogspot blogs
Lately I'm witnessing that sites do get crawled but are not shown as indexed on Google until few days or weeks have passed. Can't come to any conclusion whether its intentional on Google's part or some algorithm calculations are delaying all this.
I think there is no magical think about wordpress... the thing is that if you create a blog in wordpress.com they will link to yo uin some of their pages and since wordpress.com has a nice pagerank / reputation will Google you get an automatic benefit by receiving a link from them. If you don't add links to your blog from the outside it is just any other website... you won't get publicity. The only advantage of getting a Wordpress.com blog is that you get those links. I think that if you promote it you will get a better benefit since appearing more often in those pages (pupular blogs, recent, etc) or by making other wordpress.com blogs link to you should be a really good deal.
Wordpress is a whole lot better for my SEO than iWeb was. Plus the site is a lot cleaner and much easier to manage.