Today I don't think 6 or 8 receivers is really an unreasonable number...
Consider the modern home is so connected that there could be TVs in almost every room, so I could easily see a 4 bedroom house having DIRECTV receivers in the following rooms:
1 - Great Room / Family Room / Living Room
2 - Kitchen
3 - Bedroom 1
4 - Bedroom 2
5 - Bedroom 3
6 - Master Bedroom
So that's 6, but I know people who have the above and also have:
7 - Master Bath (above the sinks, visible from the soaker tub)
8 - Outdoor covered patio
9 - Garage
These are well-connected people, but I would think it's becoming more common to have homes with 6 or more receivers.
As the whole-home DVR receiver starts to roll out, I think it swing back the other way with there being a single centralized receiver, but homes like the one above may still require special handling...