Once again, when Bob Somerby writes, attention must be paid.
I would add a fourth explanation to his list: The commentators he skewers all arose concurrent with (and concomitant with) the post-Vietnam Democratic Party, which, as I've argued, was anti-power. Watergate was the journalistically formative experience for this generation, and it, too, was anti-power.
So consider the Hall of Shame Somerby lists: Dowd, Matthews, Kelly, Margaret Carlson, Russert, Brian Williams, Connolly, Barnicle, Gail (Gleason) Collins, Shields ... et al. Collectively, they are the scribes of the Democratic Anti-Party, the postmodern critique of politics, the oh-so-smart, oh-so-ironic journalistic institution that speaks truth to power, rather than accept responsibility for wielding it. Of course these folks are Democrats -- they dig fellow journalist-types. But of course they trash anyone who ventures into the arena -- and they reserve their deepest loathing for the Clintons... who not only found a way not to need these dispeptic fops, but rejected, in their whole being, the anti-power, immature frame that these whiplashing snidelies held as their dearest credo.
Yes, we have met them at the break of day... heard their impolite, meaningless words... seen them as evidence that we but live where motley is worn. But no terrible beauty is getting birthed 'round these parts.