1- In a business application it is quite often that one screen "Product", is checked (for its cost) at the same time as creating an invoice with discount for that product.
The ability to check this type of information is typical in a business application. nuBuilder is a business application and although its in a browser it isn't designed for browsing.
2- If you don't want too many browser windows you can also have these popups appear as tabs.
That's 2 reasons, I'm interested in knowing their objection to popups.