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 register
s, 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.