That is true that veg/seed oils are the most common, but a lot of places use animal-based mediums like duck fat and they shallow-fry instead.

I couldn't tell you if it actually tasted any better, but it's annoying as fuck when you look through the menu to find out you can only have fries for lunch, then when it's brought out the server says something like "...and our famous duck-fat fries. You like them so much it's all you wanted for lunch?"