This is an inquiry the teenaged son of a friend of mine made of the Dr Pepper people and the reply they gave him.
I don't really get the rule of grammar cited by their response but then again English grammar can be a thing of complexity so maybe I'm missing something.
I'm sure some of you erudite mudcatters can provide insights into this pressing matter.

Dear Dr. Pepper people,
> I was sipping on a very tasty Dr. Pepper one day while contemplating your
> packaging. I asked myself, why is there no period after the Dr? Without
> the period its not the abbreviation for doctor and is not pronounced
> Doctor, but Durr. Durr Pepper?
> There must have been a concious decision to make it this way. I was just
> wondering, what's that reason?
> Thanks for your time,
> Canadian Pepper Drinker


Dear Mr.******
>
> Thank you for contacting us about Dr Pepper. Your comments and inquiries
> are appreciated because they provide valuable feedback about our brands.
>
> The reason there is no dot after the "r" in Dr Pepper is becasue it does
> not refer to the title of a person. The dot after the "r" sould only be
> used when it is the title of a specific person.
>
> We appreciate you contacting us and hope you will continue to enjoy our
> brands.
>
> Sincerely,
>
> Consumer Relations
>