They don't list a 10W40 automobile oil in the Mobil 1, Mobil 1 Extended Performance, or Clean 7500 (synthetic blend) parts of their website. Looks to me as though their only 10W40s are conventional oils.
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They do make a synthetic 10W40 for a certain class of motorcycles, and an explanation of how it differs from an automobile oil and why. They stop short of saying outright that it shouldn't be used in cars, but one gets the distinct impression that it isn't meant for such service. They don't make any claims for extended drain interval with it.
Cheers,
--Joe