In practice the difference is almost non-existent, unless you start doing assignments within function calls, which is a popular style among some R stars, like Martin Machler [1]. But on the other hand some of them resolve to just always use "=" everywhere, including one of R's creators - Ross Ihaka [2].
Anyhow, explaining the difference at that part of the tutorial is not easy, so I chose to omit it for now. But might introduce it later, along with "<<-" and "->>", probably after describing closures.
[1]: https://github.com/cran/diptest/blob/master/R/dipTest.R#L37