Reader 10.0 is not a "previous version", so the Wizard is doing what the UI says it will do. Acrobat 10.0 and Reader 10.0 are now supported on the same machine. In fact, it's a good thing because Reader is more secure while Acrobat is more capable.
If you want to uninstall Reader, just do so in a separate transaction prior to running the new install.
Thank you Ben for the quick reply.
So, I take it that the recommended option would be to have both Acrobat and Reader X on the same computer. Do I need to do anything to ensure that Reader X remains the default PDF viewer?
I believe In the customization wizard for Acrobat, I need to select the option "Installer will decide which product will be the default".