Web 2.0s are simple the platform that is being offered by a certain company, that allows you to easily setup a website under their web2.0 platform. Depending on the platform, these web 2.0 can look like a blog, or a company website, or an ecommerce site, etc.
A blog is just like any ordinary blog, and majority of these would be WP based.
I think both web2.0 and blogs are pretty similar nowadays, as getting quality link juice would require to to get links from a quality web2.0 or blog that fulfill a certain metric criteria.