Sending the customer to a website is going to be quite a process for the customer.
For example instead of address + rate-lookup the QR code just contained a website URL then the customer is going to have to somehow get the information from the webpage back into their wallet app.
Let's compare the flow between using a wallet with BIP74 and using a QR with a website URL:
- Customer scans QR code in wallet app (such as mycelium)
- Enters amount (ie $3 for parking)
- Customer sends BTC (with BTC amount automatically calculated at the DRL rates)
- Customer scans QR code
- Is redirected to a webpage with form to enter the amount
- Customer enters $3 for parking
- Webpage shows address and amount in BTC
- Customer now has to try to get the amount and address into their wallet app, but seeing as they are using the webpage and wallet on the same phone they cannot scan it so have to copy/paste this into between apps (PITA)
- Customer sends BTC
Not to mention that if each merchant has their own webpage for calculating the exchange rates the customer may not be familiar with the merchants system; there is going to be some confusion each time as to what they are supposed to do. Whereas the Dynamic Rate Lookup is almost completely invisible to the customer, and they just use their wallet as they would normally use it.