That’s not exactly accurate. Once the website is complete, the OP can give the purchased product to the client, and ownership of the license transfers to them. That doesn’t require an extended license. The separation between regular and extended is whether the end users (end user isn’t the client) have to pay to access/use/view the product.
In the case of a clothes shop, an extended license isn’t required… as although the shop is selling items and making money from the site, the products they are selling are the clothes. Nobody has to pay to view the website.
In the OPs example… it’s a bit of a tough one. If the webinars came on a disk that were shipped, then that would be regular. If the end users pay to access the webinars through the site, or gain access to a paid part of the site, then it could be said that an extended license is required. Yes, they’re paying to watch videos not to look at the site, watching the videos online wouldn’t be possible if it wasn’t for the existence, design and features of the site.
So yeah, it’s a tough one. I’d lean towards you needing an extended license if end users are paying to watch the videos on the site, but I’d maybe drop an email to support and get clarification from the powers that be.