I think the particular example given has less to do with the fact that do...while is a less common control structure, and more with the syntax of do...while itself.
I suspect the referenced "slow down" was that the reader will naturally, upon encountering a loop, scroll to the end of the loop and figure out what the conditional is. Obviously the isn't really necessary in a do...while, since that code's going to run once no matter what, but I suspect most of us still do it anyway (like looking both ways before crossing a one way street).