But why not announce 9.4? 10 isn't available, so Nokia went with the latest working version of 9 - sounds sensible to me, but perhaps they didn't understand or appreciate the incompatabilities with h.264 (or considered it an insignificant problem?) It may only be an incremental update on the version shipped with Diablo, but that was from almost 2 years ago (there may have been an incremental Flash Player update released during Diablo, but not 100% sure).
There is no technical reason why it can't be updated - the only reason it won't be updated is due to corporate politics and potential licence fees (the same reasons given for not updating Flash on the 770).
Maybe someone from Nokia can give you assurances that FP10 will ship as an update for Fremantle once it is ready? Once the competing devices have FP10 I would expect it to turn up fairly soon after on the N900.