The hybrid batteries will obviously last for 100K miles, since they are warranteed for that long. Real world experience is that on average they last much, much longer.
I'm not betting on gas prices staying $3.50/gal for the next decade. The trend is up, up, up.
There is a value to predictability. When gas prices fluctuate violently, it is nice to have one's expenses more stable. Remember all the moaning here when gas recently shot to near $4? The higher your MPG, the less you notice.