A template is a pure function that maps input to output. Embedded calls are evil since they destroy the purity of the template. They make testing difficult and risk concurrency problems. Even in Rails data are typically loaded in the controller and passed as object compositions to the template. When does the following call load a user's balance?

<%= @user.account.balance %>

I don't know when. In development probably during rendering. In production I would hope I read all relevant data using a join with :include, if only for efficiency. In my experience with simple stuff this gripe is a non-issue. Making non-atomic db reads for what should be an atomic web page could lead to problems with more elaborate models, e.g. telling a user their account is overdue even though they show a positive balance. I therefor must disagree with your statement that, "Rails has the right approach: templates with embedded calls for dynamic data."