Other article spinners also require that you enter your own custom synonyms manually or individually approve lists of potential synonyms as they are presented to you. This is another way of expecting you to do most of thinking, as opposed to expecting the software to be smart enough to instantly make judgment calls for you. Thus, one of Spinbot's main goals is to make the article spinning process as quick and painless as possible.
Think of it this way: What do you have more chance of hitting, a distant, tiny target or the broad side of a barn? For the sake of search engine optimization, you want your website to be the broad side of barn. The more quality articles, or unique readable content, your website or blog offers to search engines (and therefore the general public) the more exposure your website will receive from major search engines.
Imo it is not possible for google to detect properly spun content, it is not worth computing power it requires. They can do this using ngrams for example, but it is uses a lot of queries. And for example article spinner I coded beats this algo, so google cant detect that the content is spun. Manual spinning is also good but it takes more than 30 minutes per article.