I don’t know what spammers get from this – they invest the time or hire someone to place comments and they do the spamming on blog comments. I need to mention this that these days Akismet is working fabulously.
May be I have written something about it before too – but guess needs add more to that. Spam comments are nothing but the frustrated marketers.
Most spam comments are from people who buy the crappy blog comment software and then write one comment and hit the submit button – software does all the work. With the software, you can only have one common comment written while submitting and the same is submitted to x-number of posts around the web.
Whether the comment is related to the blog post or not, it is not concerned with that. Therefore, these comments usually land in Akismet.
On an average I am getting 2 or more spam comments on my blog in a minute. Blog comments are usually a mirror reflection of your knowledge that you are either sharing or learning from someone.
Since duplicate posts are not crawled much and rank higher on search engine – same it is with duplicate comments. Therefore, if you are placing same type of comments on all blogs – basically you are landing nowhere.
Before subscribing for any such software go for manual submission. Since, this can be more helpful and perhaps you can have positive results.