Wow, then I guess we have the "ideal"! Seriously, if you architect things properly then DB changes can and should go out way ahead of the apps. DBAs are faster at their jobs than Web Devs anyway.:-)

Just make sure to nuke all select *'s (and even worse, select * into #temp) and be very careful with SPs that call other SPs for a resultset.

Only the major DB changes should need to be done in a maintenance window, like switching to nvarchars now that you have international clients.