I'd disagree with that assessment. A lot of folks purchased the 3PO well before the R2 was ever announced. That said, it comes down to your own personal taste. Sooner or later you may have to mix offerings, but anyone who's had 3PO the last 2-3 years had him as a stand alone piece until the SDCC announcement last year. I personally saw 3PO as a once in a lifetime piece and even though it pained me not knowing if R2 was coming, I still felt it was worth having this piece.
The other thing to consider is that Tamashii has metrics on sales now, so they would be smart to produce to known numbers, which would dictate having a run that doesn't result in reduced retail pricing 3 months after the release. That said, it may be easier in the future to get 3PO than it might be to go and collect R2. Conjecture.