I don't know too much about the US petrol market; but I'd say its got something to do with market concentration. Lower rates of competition.
These companies are vertically integrated (AFAIK), so they control the product from refinement to pump, so they get to set their wholesale prices as well as their retail prices.
Finally, "crude" prices which you are referencing are likely spot prices, not necesserally a reflecting of contract prices between extractors and refiners.
In Australia, we've only really got three (at a stretch four) retailers who have control over distribution, who have formed this "weekly pricing cycle" where prices rise higher at the beginning of the week (usually a Tuesday) and progressively fall over the week only to spike up again. Its basically tacit collusion, but the Government doesn't acknowledge it as such.