A friend of mine is a product engineer for one of the largest (the largest?) makers of RTC chips.  He groans about the (rather pointless) quest for the lowest power RTC chips.  Making robust, stable, accurate oscillators that run at nanowatts is a losing proposition.  At those levels external factors can wreak havoc.  And he blames crystal makers for a lot of problems... batch X works great,  batch Y is wonky,  batch Z is utter crap.  Pretty much the same for load capacitors.  Eventually users come to their senses and go with a robust, slightly higher power device.