The $5 transaction fee creates a floor for transactions. If other processors charge a 2% fee, then it doesn't make sense to use Bitcoin to transfer funds or use for purchases lower than $25. This already blocks a huge array of daily transactions, including a $20 ATM withdrawal and probably lunch.

Additionally, there is a floor to the fractionality of Bitcoin, of 100 000 000 Satoshi. If Bitcoin ever reaches $1,000,000, then it could only be divided into $0.01 denominations, and not further. If it reaches $2,000,000, then 1 Satoshi would be worth 2 cents.