Huh, whaddya know. There it is right there in the XML:
<Row>
<Type>POLICY_ENTREPRENEURSHIP</Type>
<Description>TXT_KEY_POLICY_ENTREPRENEURSHIP</Description>
<Civilopedia>TXT_KEY_POLICY_ENTREPRENEURSHIP_TEXT</Civilopedia>
<Help>TXT_KEY_POLICY_ENTREPRENEURSHIP_HELP</Help>
<PolicyBranchType>POLICY_BRANCH_COMMERCE</PolicyBranchType>
<CultureCost>10</CultureCost>
<EmbarkedExtraMoves>1</EmbarkedExtraMoves>
<GridX>2</GridX>
<GridY>2</GridY>
<GreatMerchantRateModifier>25</GreatMerchantRateModifier>
<TradeMissionGoldModifier>100</TradeMissionGoldModifier>
<PortraitIndex>3</PortraitIndex>
<IconAtlas>POLICY_ATLAS_EXP2</IconAtlas>
<IconAtlasAchieved>POLICY_A_ATLAS_EXP2</IconAtlasAchieved>
</Row>
I guess that means Merchants of Venice don't really have a bonus to embarked movement. I would play games and pick this policy all the time with the good Doge, and otherwise ignore it.
Maybe it's supposed to represent your civilian units "getting around" on their own capital or something...