Not at all, its a very common requirement for anyone who wants to do LOB + website frontend with a CMS, but its not doable in most if not all CMS's out there, I think only 1 or maybe 2 have this. Its also common in ecommerce.
This is the scenario I was searching for as I found this post:
We want to create a new Role on the site called "Sales", then we need a new Content Type called "Product" which has a Content Part called "Price" attached to it.
Now the requirement is that the "Price" is not viewable on the frontend for Anonymous or Authenticated, but is viewable by the "Sales" role, and for simplicity and convenience it is only editable by the Editor or above role.
This way we can effectively maintain a company site frontend with a bit of extra info for the employees without the need to create 2 separate content types.
Can this be done with writing a custom content part?????
I must say that Orchard in its un-modded form is already very powerfull CMS, you have to install at least 5 plugins for wordpress to get the same stuff.