The metapackage exists to refer to the existing version-specific version of the full package. For example, linux-image-generic
will point to linux-image-3.2.0-101-generic
or whatever the latest-updated kernel is.
The metapackage is version bumped to point to the latest kernel version with each update. By installing a specific kernel, and then not relying on the metapackage for your kernel versions and updates, you get no updates.
Each individual update to the kernel, either a critical bug fix or a security fix, requires a new kernel package to be created, and the metapackage bumped. There is no way to automatically backport 'fixes' to all the older package versions, as the kernels are considered 'different versions' at that point.
If you remove the metapackage and rely only on a specific kernel package, you get no security updates, no bug fixes, and you may actually have difficulty upgrading in the future (if you attempt an in-place upgrade).
You should not remove the metapackage, and should keep it in the system. You also must install new kernel images to get security updates on the kernels.