is more about where the code / processes run, and n-Layer
is more about how the code is logically grouped (BLL, DAL, Presentation layer).
We can talk about nopCommerce as 3-Tier application, if we talk about an user browser, IIS, and database. They all run on 3 separate physical machines, each separated by a network. This way nopCommerce
But I was talking about plans to support separating BLL, DAL and presentation layer to separate physical machines.