Peter, we share your frustration with this and would like to do the
same thing. I've got no insight to offer regarding that, but your
comment about the "laborious task of deleting meeting site
instances" might be eased if you have the URLs of each of those in a
list. You probably already know this and it's not much, but it does
speed things along.
If you have the URLs of the sites somewhere in a list, create a
calculated column with the formula
="http://portalname.company.com"&URL&"/_layouts/1033/deleteweb.aspx"
and add it to a view of the list.
As long as you don't have spaces in your URL, your browser should
recognize and activate the hyperlink. Make sure to hold down the
<SHIFT> key when you click so it launches in a different browser and
you don't have to navigate back. This link will bring you to the
delete site confirmation screen.