"If you are charging a fee for access to your Maps solution, whether for a business or consumer audience, you are required to purchase the Maps API Premier."
To me this reads as, any SAAS web app which used a Google map anywhere would be required to pay $10,000 per year plus usage charges.
You can use it on a commercial site, but the maps implementation must be available to free users. It limits your options but there are plenty of sites that are commercial ventures and work within these limitations.
When I dug deeper, it appeared, at the time, that this only applied to features of the app that required payment. So, we were free to offer maps features on our site as part of our free offering. We could still have premium features without paying for a premier license, so long as those premium features didn't rely on Google maps.