Investors generally aim for a 10x+ return, so if an investor invests $3m at $10m pre-val they'd be aiming for a $100m+ exit.
They're definitely not only aiming for $1bn+ exits although obviously they're a bonus (in the last decade there have probably been under 50 billion dollar exits in the tech space).
PG is an investor and he has stated multiple times that he'd prefer that all of his investments were aimed at the high end of the range of possible outcomes (mentioning Google's exit more than once in this context). Of course he has also stated that he understands that it is usually not in the best interests of the founders, so no pressure.
They're definitely not only aiming for $1bn+ exits although obviously they're a bonus (in the last decade there have probably been under 50 billion dollar exits in the tech space).