1. Google has to return a result count.
2. It can't/won't be accurate.
3. Therefore it's fine to provide a count 10 billion times to large.
The jump from 2 to 3 is dodgy and I see people questioning it. But I don't see anybody challenging point 1. Why does google have to give a number at all? If google can't/won't give an accurate result count, then they should give a result count at all. I don't care what technical limitations might complicate giving an accurate result count, that's no excuse for lying when silence is a perfectly valid choice.
Obviously they provide the count for marketing reasons. That's an explanation for the lying, but not an excuse.