Yes, that is correct. The PowerStore is setup to allow you to make the shipping choices in the admin section, then based on your choices shipping quotes will be returned on the confirm page to show charge for the shipping.
You can add in the ability to use other shipping options with eCart. If you would like to have the user select a service type you will need to add this option to the checkout page. There are snippets in eCart for these select lists. You will need to ensure that the select list is placed inside of the checkout form.
The select list can be added to the page from the snippets, go to Window > Snippets, in here find eCart and expand it then look inside of shipping. You should see the entries for the service type select lists. Once you have added the services select list you can use the lightning bolt icon to select this form element for the service type in the shipping quote server behavior on the confirm page.
Giving the user the choice of shipping providers is more involved and requires some custom coding.
