Does obscured vision affect speed?

Question

Obscuring mist makes no mention of speed and to my knowledge not being able to see more than 5 feet in front of you has no effect on your movement whatsoever, is this correct?

Answer 1

Hampered Movement

Difficult terrain, obstacles, or poor visibility can hamper movement. When movement is hampered, each square moved into usually counts as two squares, effectively reducing the distance that a character can cover in a move.

If more than one condition applies, multiply together all additional costs that apply.

From PHB p.163 or SRD.

Answer 2

The rules on Hampered Movement (PH 163) mention that "poor visibility can hamper movement [so that] each square moved into usually counts as two squares." Further, Table 9–4: Hampered Movement has "[d]arkness or fog" as the only examples of poor visibility (ibid.).

However, the Dungeon Master's Guide on Fog doesn't list reduced movement among its effects:

Whether in the form of a low-lying cloud or a mist rising from the ground, fog obscures all sight, including darkvision, beyond 5 feet. Creatures 5 feet away have concealment (attacks by or against them have a 20% miss chance). (94)

Further, the 1st-level Sor/Wiz spell obscuring mist [conj] (PH 258) doesn't mention reduced speed among its effects, either, nor does the 2nd-level Sor/Wiz spell fog cloud [conj] (PH 232).

With this in mind, this DM has never played that a creature that can still see—even only 5 ft. in front of it—has its movement hampered, nor has this player been in a campaign where the DM ruled that way. It's entirely possible that movement is supposed to be hampered in such circumstances—and that's supported by the rules—, but I've never had a DM put that particular 1 from the PH on hampered movement due to poor visibility and that other 1 from the DMG on fog together to get that particular 2.

Nonetheless,—maybe because hampered movement is mentioned explicitly by such effects,— a creature that's blinded or effectively blinded due to environmental circumstances—like being in absolute darkness through which the creature cannot see—does find its movement hampered.