The University of Chicago Manual of Style, Fifteenth (newest) Edition disagrees with Topsie on all counts, pp. 560 - 568.

While the military , ever in the forefront of good grammar, has now stopped using periods for rank, ie. ADM, CPT, GEN, the manual advises writers to use the old style with periods to avoid confusing readers.

Most likely, the lack of a period in Dr Pepper is a legalism to prevent literate persons from thinking the beverage is medicinal.

Good words to all - Tom