Its true that a thinner oil will reach the lifters better but its mainly important for cold starts. Even a 60 weight is just fine when warmed up. The main reason they spec 30 weight in the US is due to CAFE regulations and its used since most engines will go the entire warrany period without issues. Your link mentions HTHS which is measured at 150 degC. Have a look at the huge difference in HTHS between a 30 and 50 weight. The owners manual was recommending an ILSAC GF2 rated oil which is an eco spec (ILSAC GF spec is labelled "resource conserving"). Otherwise use 15w40 or 20w50 so the initial 30 weight recommendation is purely for fuel economy reasons.