It has been a long time since I started this topic, and in the meantime, I've had an opportunity to try different kinds of topre keycaps -- namely default Realforce, blank HHKB's, all kinds of hand crafted artisans etc.
So, I finally feel competent enough to answer my own question from the first post in this thread.
Yes, there is definitely minute difference in quality between Realforce and HHKB keycaps.
They are both made of same PBT plastic and they are both obviously made based on the same specifications; however, it seems to me that they are actually not made in the same factory, or under same quality control process.
There is this guy right above my post that claims feeling of typing changed slightly when he put HHKB keycaps on his Realforce. I've done the same thing and I can not confirm this. I'm not saying this is necessarily untrue, I just can't tell even if it is. To me, it feels completely the same. If there is any difference, it must be either a placebo or something so slight it's nearly impossible to detect even after months of use.
However, there is something else that bothers me about HHKB keycaps, and that is aesthetics. Almost all of them have circle impressions on the upside, right above (and in the same shape of) the stem. You can easily see on the pictures what I'm talking about. This is a real disappointment, and I've seen the same problem on various cheap Chinese PBT keysets. I'm going to have to guess and tell that they let them cool down too quickly, and thus they shrank too fast, leaving this kind of traces. Absolutely none of the default printed Realforce keycaps had these circle impressions, and almost all of HHKB keycaps do.
