Just a thought and only a thought, no concrete bases to say this is a fact.
Being a past collector of coins I would consider a "pretty penny" as an uncirculated coin with no blemishes and having distinct stampings. Coins that have not been circulated is always desired by collectors since they have greater wealth attached to them. The coin is usually always worth more than its face value. And who would have with them such a coin? Certainly not the common folk of old but those who had the opportunity to mingle around those in financial institutions, which I believe were off limits to those without wealth and some level of standing within the community.
Again, just my thoughts.