In point of fact,
RPN is used to this day in
Hewlett-Packard electronic calculators because it was much easier to
implement than the more
linear forward notation when the electronic calculator was new. A
stack-based system (such as RPN) is more
efficient (especially for the machine) and minimizes the use of
randomly-addressable registers, which are more costly to implement (at least, they were then).
To this day, HP has managed to maintain the Cult of RPN - as can be seen on E2 and elsewhere, 'real (insert number-crunching profession here) use RPN' is a common theme when the subject comes up. Essentially, it was (and remains) a tradeoff; forcing the human to use an (initially) unfamiliar schema which was closer to the more efficient algorithms of the machine.
Before the flaming starts, please note that I have no opinion about which is 'better.' Once learned, RPN can, in fact, be more efficient than forward; it's a matter of taste. The Cult of RPN is akin to the Cult of Macintosh - there is always a small percentage of adherents to the system that vociferously claim it's better 'just because.'
Of course, the Germans, never ones to be slackers about anything, then went and built a conversational language around it. Go figure.