One explanation I've heard for the PDF menus is that they have to have PDF versions anyway for printing, so the least-effort solution is to just put the same PDFs online.
In my experience having worked with restaurants, websites, and menus, they most often have humongous Publisher or Word files. PDF is the easiest form to coerce the content into while still retaining some degree of the original formatting. Oh, and they're also notorious for changing the menus constantly.
If they can't be bothered to run the PDF through a program to translate it to HTML, and then post a link to the PDF version, I don't want to do business with them.
If their menu is so fancy that it can't be easily translated into HTML, they're missing the point entirely.
Well, good luck with that approach, I guess. Personally I care a lot more about the quality of the food, the quality of service, the cleanliness of the restaurant, the ambiance, the price, ...
If I'm trying to order food from them, and their entire business model depends on me buying food from them, yet they're making it hard for me to find what food I can buy from them, they are either idiots or sloppy people who hire idiots to design their website. Either way, they're worthless.