Your not missing anything. Infusionsoft doesn't perform validation on those fields. You'd need to add in some of your own javascript to validate the form.

Here is a how to on adding that javascript to your form. It's a little painful but it's what I use every time I'm asked to do that...
http://www.w3schools.com/jS/js_form_validation.asp

This validation has nothing to do with Infusionsoft but if you set it up right, it should check your form before it's ever submitted to Infusionsoft keeping your data clean.

Cheers!