I've had my HS250h since 10/17/2009. My experience has been that getting a 100% charge is infrequent. It usually only happens if I've had to use the brakes quite a bit and the pack is already "mostly" charged.
I don't worry about it ... just try to make sure it's "sufficient" (>50-60%) to take advantage of the hybrid modes. I try to keep it >60% unless I'm using EV for the end of my drive in our neighborhood. For my vehicle, "charged" is usually between 80-90%.
My previous hybrid behaved very similar and I agree w/Argelius that this is "normal" behavior.