Not all bloggers, for sure. But there are quite a few whose work would qualify as journalism -- in the sense of reporting -- of both news and investigative kinds. Want some examples? Take a look at journalism professor Jay Rosen's stinging response to a clueless op-ed in LATimes. Among the examples, this is my favourite:
2003 to present. Groklaw becomes the go-to source for coverage of SCO vs. IBM. Law blog -- one obsessive blogger, plus readers -- takes on saturation coverage of key lawsuit involving open-source software, becomes an authoritative source of knowledge for the case's participants, who have never seen anything like it.