Perhaps a naive question:

I have a large complex Windows application. I want to replace the existing InstallShield (non-MSI) installer. Why not to write a simple GUI program in c# to do this job? Instead of dealing with MSI/Wix, etc. My target computers all have .NET 4.0 installed – I am thinking a simple Winforms GUI. What is MSI/WIX giving me that would be hard to do in c# ?

My installer needs to:
copy some files
manipulate registry entries
create shortcuts
install drivers (using existing 3rd party installers)
cleanly uninstall the previous version
store somewhere the current version

Did I forget anything? All the above is easy in c#. Am I overlooking something?