Kangarooo and Srinath: Ah ha, I get what you are on about now. My test system here doesn't have that package because of the same issue :-)

This is now fixed. The script should now only ever remove packages that match this pattern
"linux-image-|linux-headers-|linux-backports-modules-"
*and* show up in the 'dpkg -l' output as a 3 dotted number followed by a dash. This should prevent removal of the package that triggers updates (as it shows up as a 5 dotted number)

The running kernel is now never removed either, just as with the last-good-boot kernel (if present).

There is also an option to run the command.

I've also tweaked the output:
$ ./remove-old-kernels
/etc/kernel/postinst.d/remove-old-kernels:
Reading system config file /etc/remove-old-kernels.conf ...
Found last-good-boot, 2.6.32-23 will never be removed
Current kernel 2.6.32-24 will never be removed
Installed kernels 2.6.32-21.32 2.6.32-22.36 2.6.32-23.37 2.6.32-24.42
Older than top 3: 2.6.32-21.32 
Will remove packages for 2.6.32-21.32
Suggested command is ...
sudo apt-get remove linux-image-2.6.32-21-generic
$

if I change my number to keep:

$ ./remove-old-kernels
/etc/kernel/postinst.d/remove-old-kernels:
Reading system config file /etc/remove-old-kernels.conf ...
Found last-good-boot, 2.6.32-23 will never be removed
Current kernel 2.6.32-24 will never be removed
Installed kernels 2.6.32-21.32 2.6.32-22.36 2.6.32-23.37 2.6.32-24.42
Older than top 1: 2.6.32-21.32 2.6.32-22.36 2.6.32-23.37 
Will remove packages for 2.6.32-21.32
Will remove packages for 2.6.32-22.36
Nothing can be done with 2.6.32-23.37
Suggested command is ...
sudo apt-get remove linux-image-2.6.32-21-generic linux-image-2.6.32-22-generic
$

This is with what I hope is a more normal set of packages (note 'linux' and 'linux-generic'):
$ dpkg -l | grep ^ii|  grep 2.6.32
ii  linux                                                                        2.6.32.24.25                                         Generic complete Linux kernel.
ii  linux-generic                                                                2.6.32.24.25                                         Complete Generic Linux kernel
ii  linux-headers-2.6.32-23                                                      2.6.32-23.37                                         Header files related to Linux kernel version
ii  linux-headers-2.6.32-23-generic                                              2.6.32-23.37                                         Linux kernel headers for version 2.6.32 on x
ii  linux-headers-2.6.32-24                                                      2.6.32-24.42                                         Header files related to Linux kernel version
ii  linux-headers-2.6.32-24-generic                                              2.6.32-24.42                                         Linux kernel headers for version 2.6.32 on x
ii  linux-headers-generic                                                        2.6.32.24.25                                         Generic Linux kernel headers
ii  linux-image                                                                  2.6.32.24.25                                         Generic Linux kernel image.
ii  linux-image-2.6.32-21-generic                                                2.6.32-21.32                                         Linux kernel image for version 2.6.32 on x86
ii  linux-image-2.6.32-22-generic                                                2.6.32-22.36                                         Linux kernel image for version 2.6.32 on x86
ii  linux-image-2.6.32-23-generic                                                2.6.32-23.37                                         Linux kernel image for version 2.6.32 on x86
ii  linux-image-2.6.32-24-generic                                                2.6.32-24.42                                         Linux kernel image for version 2.6.32 on x86
ii  linux-image-generic                                                          2.6.32.24.25                                         Generic Linux kernel image
ii  linux-libc-dev                                                               2.6.32-24.42                                         Linux Kernel Headers for development
$