Not all the funds are that high. The .18% vanguard quotes is their real, across customers, result. Their more active funds are higher (like VEXPX at .49%) while their larger scale Admiral funds are often as low as .05% (like VTSAX).

Vanguard ETFs offer the same rates as the equivalent Admiral class shares, so services like Wealthfront use those. Wrapping Vanguard is a lot easier these days ;)

Institutional class expense ratios are much lower than 0.18% average. Also, they can pick the lower cost funds.