A lot of people use WordPress BECAUSE it can be optimized easily for SEO. Their permalinks are great for keywords in the URL. Also, there are great internal linking structures (like Previous/Next Post and Related Posts plugin). Also there are A TON of great plugins that make Technorati tagging, Title Modifications (to make the post title come first) easy and such...
wordpress is good and i think u can go for blogger.com also. My blogs in here have been cached by google