The thing is, the issues with the search engines would be the same no matter where you blogged, because it isn't something that is within your control. You can keep search engines from crawling and indexing your blog, but you cannot keep them from finding you via a link on another blog or site. All it takes is one link even in a comment made by you on another blog. You linked your username to your blog and every time you leave a comment on a wordpress.COM blog, that link is there. If you comment on another blog and leave the URL of your blog when you do, a link to your blog is there.
Even if you set your blog to private, all it would take in one link to it somewhere on the internet, and there is a high likelihood of your blog being listed on search engines. There would not be any details with the link - since your blog was set to private - but it would be there.
The bottom line is there is no way to stay completely under the radar on the internet. It simply is not possible, and again, it has nothing to do with where you blog, or what platform you use.