I think that would be good because frequently I've seen people who think that address which is being shown there is the bitcoin addresses of theirs. Like if there were only one, as a bank account number. This happens frequently.
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.
I propose an alternative: instead of having a "New..." button next to the address, make it an "Add..." button (with tooltip "Add new receiving address"). This makes it clear that the old address is not being replaced.
And maybe change "Your Bitcoin address" to "Current Bitcoin address"?
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...