How Weird Is Baseball?

Here are some weird pitching stats that don't seem to add up. For all you stats geeks, tell me how this works.

Edwin Jackson: 2-3 but a 3.29 ERA
Felix Hernandez: 2-4 but a 3.34 ERA
Aaron Harang: 2-6 but a 3.50 ERA

A.J. Burnett: 5-4 with a 4.69 ERA and a terrible offense
Andy Sonnanstine: 6-2 but a 5.09 ERA

Brian Wilson: 14/16 in SVO but a 5.49 ERA

Gavin Floyd: 25 K and 27 BB but 4-2 with a 2.93 ERA
Fausto Carmona: 23 K and 38 BB but 4-1 with a 3.10 ERA