I'm not sure where you ran across those, but here are my thoughts on what the source may be thinking:
> 1) Potential network bottleneck;
I agree with you that there isn't really a difference in the network communication between client and the x-tier application, but they may be referring to potential network limitations between the tiers of the 2-tier application vs. the tiers of an n-tier application; there are inherently less network 'hops' or 'paths' between tiers in a 2-tier application vs. an n-tier application and if you assume the same horizontal scalability in each tier, there would be more network traffic on each of the between-tier hops/paths in a 2-tier app
> 2) poor scalability. As the business is tightly coupled with data store.
I agree with you that the typical Sun definition of hardware 'scalability' is not what they are referring to - I think they're referring to scalability of the components or modules of the application itself, as the application is not quite as modular or loosely-coupled as is preferred (with only 2 tiers, the business logic is inherently more tightly-coupled with the data store than in an application with > 2 tiers)
Hope this helps...
-Steve-
