Depends how you take what was posted. "8MB/s on a download and 5MB/s on supernews", sounded like one protocol to me, being the latter.
Discounting the latency as that can happen for many reasons when pushed. It could even be a dodgy router not able to cope with multi threaded applications. Of course, thats based on the assumption that the other download at 8MB is single thread as is common for a download (gone are the days of things like GetRight, although i'm sure someone still uses it, somewhere) and the NNTP data is multi thread.
We've seen an increase in routers that have QoS/bandwidth management enabled by default, or when manually enabled the defaults are not great causing very odd behaviour.