True but this would indeed be considered very unusual and surprising for software if it wasn't indicated explicitly.

I just checked and while they do only indicate "X €/month" on the product page, as soon as you enter the checkout process it says "yearly subscription, monthly payment - Y €/month" with the additional options "yearly subscription, advance payment - X €/year" and "monthly subscription - Z €/month". I'm not sure how they're getting away with the misleading prices on the product pages tho (usually there's at least an asterisk indicating this comes with additional conditions and obligations).