Well, i didn't figure to find a proper solution to this issue...
I will just let the user to complete delete a product from the cart by putting "0" to the quantity field.
But i am afraid that the code the "shopping cart display" is not 100% correct or compatible...
I have done the following from scratch:
1. I have edited the e cart object to fit my needs in euros and kgs.
2. I have then gone to display manager and changes the colours etc.
3. I have added a "remove" checkbox column.
I saved it and everything looked ok. But the code that it generated for the checkbox contained the name WA_Store_Cart_Delete and not WA_Store_Cart_Quantity_check as you said it shoul have. And it also did not generated any hidden form element.
I tried to chenge these settings manualy at code view by copying the code from the original powerstore cart.php file and pasting it into the new file. but it didn't work either...
One thing i noticed is that the layout generated by display manager contained the checkbox within a table and not a <div> like in the original cart file. I do not know if it plays a role.
I would like some further suggestions because i am quite unhappy for offering the e-shop visitor a poor solution to remove products.