Only advantage I can see to typeof directly is possibly a slight performance gain, but I don't think we are even at the point of worrying about those sorts of optimizations :)

(The numbers are a bit instance on my machine but again I don't think we are running this anywhere where we have the sort of looping that this is a concern. Rendering the DOM that is involved with these checks is going to have a much higher performance impact)
http://jsperf.com/isstring-vs-typeof-string/2