>I can't beleive they don't at least expand to the largest width value.
In a normal HTML web page it would. I strongly suspect your .NET report is formatting the length of the drop down list with CSS. Most .NET editors have the developer drag and drop the controls onto a grid, then apply absolute positioning to the elements. It's a horrible way to format pages but hides the CSS from the developer and lets non-experienced developers make pages quickly.
Check the element in your development tool and see if it is being assigned a fixed width.
In normal HTML, even if the list is shortened using CSS, the list will expand when clicked to show the longest value. Ideally, you can figure out how to use a normal HTML
