"neutral expression" is probably a better way of putting it, rather than "expressionless". Partly it's down to the artist but some of it has to be the input of the license holder and the personality whose portrait it is. It does seem to be the norm, with some notable exceptions (Aldo, King Leo alternative HS; Bruce Lee DX and MIS; Jack Sparrow alternative HS (maybe); Comedian etc).
With most characters it's fine, but for some it's a missed opportunity to really capture the essence of a character, ie Hans Landa. I think that, details aside, Arnie has got a good expression going on with Indy. If he revises this sculpt but retains something of this expression we'll end up with a great representation of Indy. I hope.