Who cares? It's the quality of Welch's research that matters. I have no idea whether or not Matt is biased against Paul, but if he is and his bias leads him to do work that withstands scrutiny, then the motives don't really matter. Facts are facts.
If the person who turns you in for a murder you committed is your sworn enemy, you still go to jail.
People who consistently misreport reality, for reasons of bias or incompetence, deserve the bad reputations they earn. At some point, readers will stop paying attention to them. But alleging bias, or even identifying it, is not enough. Facts are facts.
This pattern of shooting the messenger repeats itself endlessly on blogs. A prime example was the "You hate Bush" retort to critics of the Iraq war. While "hate" is a loaded word, certainly a lot of critics thought Bush was a bad president. So what? Events proved the critics right: after misspending years, lives, and dollars in Iraq, Bush ended up replacing Rumsfeld, sending more troops, and so on. Maybe if the you-hate-Bushers had paid attention to the facts on the ground, instead of just challenging the motives of critics and pretending things were OK, the administration would have been forced to make necessary changes sooner.
Sometimes the results of bias-hunting are unintentionally funny -- check out Guarino's attempt to discount Jordan Green's analysis of the Bledsoe series by pointing to the liberal slant of Yes! Weekly. That slant is real enough, but to use it to deflect Green's reporting is weak, and to do so without mentioning the conservative slant of the Rhino, Bledsoe's well-documented antipathy for the N&R, etc. is just absurd. All those factors may motivate the players -- but in the end, the play's the thing.
Judge the work on its merits.