Hm you have a point. On the other hand I think it's very useful to have an address on the main page, and you can quickly copy it and give it to someone.
The recommended way to use bitcoin is by creating a new address for each receipt. Somebody following this practice will already have to click a button to generate a new address in a new window. In this window it's already possible to copy it to the clipboard.
I don't think the behavior of not following this practice should be facilitated by the client, as it is today, by making the last address there, available to be copied and reused.
Or change it to a combo box if there are multiple receiving addresses, so you can directly select which default address you want? That's probably most clear...
Wouldn't a combo become too big eventually? Anyway, if it is easy to filter by the address label I suppose that's not a problem.