I wouldn't say there is any higher potential for fraud, as they're essentially verifying the same about of data. It may make it slightly more difficult to recover funds if your card is used without your permission, however.

The processing rate is typically lower because of agreements between issuing banks and debit processing networks, and is a somewhat hot topic at the moment as technically pinless online debit transactions are only intended for when the customers identity has been "confirmed", such as individuals with running accounts at a wireless carrier.

However, for whatever reason, some big companies are being allowed to use the MasterCard Debit/Maestro/Visa Debit/STAR/PULSE networks in this manner. In this case that company is Starbucks.

I'd estimate the rate paid by Amazon/Starbucks for processing pinless debit is 0.8% or less. Compare this with the 0.9 - 2.2% interchange fee (depending on card type) they'd incur if they processed these transactions as credit. It might not sound like a lot, but at that scale it probably ends up being millions per day saved.

It's not pinless debit versus regular debit, but rather pinless debit versus credit.