The compiler can't necessarily optimise i++ away in C++, because the ++operator or the destructor of the temporary iterator object returned may have side effects. It's still not quite equivalent to ballards postincrement() though, because the C++ standard allows for that temporary copy operation to be optimised away
Compilers are sometimes smart enough to remove the unnecessary operation in C++ (e.g. switch to ++x themselves), but I always use ++i for the same reason people simplify their usage of C in between sequence points --- it's an easy transformation, and why tempt fate?