NFS sucks

Why isn't it possible to unmount a NFS share if the IP-address of the NFS-Server has changed? Today I had a situation where a client hosting a NFS filesytem which is being mounted on one of my AIX boxes died. Every ls command in the mount point resulted in either long timeouts or I/O Errors which drove one of our FAM-processes crazy. So I had to unmount the filesystem to ensure the functionality of this process. That was impossible, because the host was not up anymore and so I couldn't unmount the filesystem. What really helped then was to bring up a secondary interface with this hosts ip-address (it was down at this time anyway) on my client machine. After doing so, I was able to unmount the NFS share (just to mention, my client does not understand a word of NFS) by just bringing up the ip-address again. Where's the damn sense in that?