No, it appears that this is confirmation bias on the part of the users and in fact, Nintendo warns not to do so:
Do not blow into your Game Paks or systems. The moisture in your
breath can corrode and contaminate the pin connectors.
This statement by Nintendo has been backed up by non-scientific testing1 which has shown that blowing on the cartridges can cause build up on the connections which could theoretically interfere with the connection.
Now, with regards to the claims of blowing on the cartridge itself, I would first like to note that some searching around showed that most people don't recall hearing of anyone making this claim prior to the introduction of the original Nintendo Entertainment System (NES) nor does it seem to arise with later systems such as the Nintendo 64 which was also a cartridge based system.2 When industry experts are interviewed they tend to say that blowing on the cartridge would only really help in the case of dust on the cartridge and the rest of the time it was likely a "placebo effect"3, the following quote is quite telling:
1.) The act of removing, blowing in, and re-seating a cartridge most likely creates another random opportunity for the connection to be
better made. So removing the cartridge 10 times and putting back in
without blowing on it might net the exact same results as blowing on
it between each time.
Finally, the real issue with the NES was one of a fundamental design flaw with the design of the zero insertion force (ZIF) connection, as summarized by Wikipedia:
The newly designed connector worked quite well when both the connector
and the cartridges were clean and the pins on the connector were new.
Unfortunately, the ZIF connector was not truly zero insertion force.
When a user inserted the cartridge into the NES, the force of pressing
the cartridge down and into place bent the contact pins slightly, as
well as pressing the cartridge’s ROM board back into the cartridge
itself. Frequent insertion and removal of cartridges caused the pins
to wear out from repeated usage over the years and the ZIF design
proved more prone to interference by dirt and dust than an
industry-standard card edge connector. These design issues were
not alleviated by Nintendo’s choice of materials; the console slot
nickel connector springs would wear due to design and the game
cartridge copper connectors were also prone to tarnishing.
This is also a major factor in the Model NES-101, or the Top Loader. Which introduced a top loading cartridge slot that eliminated the need to force the connection and thus the wear and tear on it.
Thus, to summarize: blowing on the cartridge likely only works in the case of dust on the connections which is likely fairly rare; however, the act of doing so gives another opportunity for a good connection to be made which allows for a confirmation bias to arise. The underlying problem though, was a design flaw with the connector that allowed it to degrade and break down over time due to wear and tear.
- Non-scientific from the standpoint that the sample set is not large enough to make proper conclusions from; however, it does provide a nominal example of confirmation of Nintendo's claims.
- There is no good way to source this as it is a summary of what I read in various forums and discussion sites and should be treated as anecdotal evidence at best.
- Most likely a confirmation bias is what was actually meant by the individual interviewed.